Model and nonlinear dynamic analysis of linear guideway subjected to external periodic excitation in five directions

Nonlinear Dynamics - Investigation of the dynamic characteristics of linear guideway is essential for enhancing structural performance of machine tools. However, few mechanical models are...     

Asymmetric Synthesis. VII. Double Stereodifferentiation in Allylation of Ketimines Bearing Two Chiral Auxiliaries. Application to Enantioselective Synthesis of α-Allylglycine

A double asymmetric induction has been observed in allylation of the imines derived from (+)-camphor, (+)- and (-)- 2-hydroxypinan-3-ones with (+)- and (-)-menthyl glycinates. After hydrolysis of the allylated intermediates, (R)- and (S)-α-allylglycines are obtained in 3–90% optical yields.     

Estimation of the Reliability of a Stress–Strength System from Poisson Half Logistic Distribution

This paper discussed the estimation of stress-strength reliability parameter R=P(Y<X) based on complete samples when the stress-strength are two independent Poisson half logistic random variables (PHLD). We have addressed the estimation of R in the general case and when the scale parameter is common. The classical and Bayesian estimation (BE) techniques of R are studied. The maximum likelihood estimator (MLE) and its asymptotic distributions are obtained; an approximate asymptotic confidence interval of R is computed using the asymptotic distribution. The non-parametric percentile bootstrap and student’s bootstrap confidence interval of R are discussed. The Bayes estimators of R are computed using a gamma prior and discussed under various loss functions such as the square error loss function (SEL), absolute error loss function (AEL), linear exponential error loss function (LINEX), generalized entropy error loss function (GEL) and maximum a posteriori (MAP). The Metropolis–Hastings algorithm is used to estimate the posterior distributions of the estimators of R. The highest posterior density (HPD) credible interval is constructed based on the SEL. Monte Carlo simulations are used to numerically analyze the performance of the MLE and Bayes estimators, the results were quite satisfactory based on their mean square error (MSE) and confidence interval. Finally, we used two real data studies to demonstrate the performance of the proposed estimation techniques in practice and to illustrate how PHLD is a good candidate in reliability studies.     

功能微粒材料的制备及其细胞作用研究(英文)

随着纳米科学的迅速发展,越来越多的微粒材料被设计和制备出来,并应用于生物医学领域,取得了令人瞩目的进展和成就。近年来,我们课题组发展了一系列具备可控表面化学与结构、特定刺激响应性能和可控装载与释放性能的微粒材料,尤其是基于层层自组装的中空微胶囊。同时,我们也致力于研究微粒材料与细胞的相互作用,阐明其物理化学性质对细胞内吞和细胞功能的影响。通过这些研究,我们希望进一步建立功能性微粒材料的生物学功能优化的规律,推动其在生物医学领域的应用。     

Nonlinear dynamic characteristics of ball screw feed system under thermal deformation

In this study, a novel kinetic model is established to investigate the dynamic characteristic of the ball screw feed system by considering the thermal deformation of bearing joints, screw-nut joints and screw shaft. Based on the Hertz contact theory, the relationship between elastic restoring force and axial deformation of bearing joints and screw-nut joints is obtained, respectively. Then the dynamic characteristics of the kinetic equation are analyzed by Runge–Kutta method. The vibration characteristics of the feed system with and without thermal deformation are analyzed, and the results indicate that the amplitude becomes larger when thermal deformation is considered. The motion state of the feed system at different frequencies is analyzed, and the results show that with the change of frequency, the motion state of the system will appear period-doubling motion, quasi-periodic motion and chaotic motion. Finally, the influence of different parameters on the vibration characteristics of the system is discussed.

     

Asymmetric Syntheses IV: Enantioselective Synthesis of (R)-Benzylic Amines Via Alkylation of D-Camphor Ketimine

An efficient asymmetric synthesis of (R)-benzylic amines in optical purity 36–90% had been achieved by alkylation of a chiral ketimine prepared from D-camphor and benzylamine. Diastereoselectivity in the alkylation is dependent on the alkyl halides.     

Well-posedness for the heat flow of harmonic maps and the liquid crystal flow with rough initial data

We investigate the well-posedness of (1) the heat flow of harmonic maps from \mathbb Rⁿ{\mathbb R^n} to a compact Riemannian manifold N without boundary for initial data in BMO; and (2) the hydrodynamic flow (u, d) of nematic liquid crystals on \mathbb Rⁿ{\mathbb R^n} for initial data in BMO⁻¹ × BMO.     

生物材料表面性能调控骨髓间充质干细胞分化

结合细胞和生物可降解支架的组织工程和再生医学技术为组织、器官的修复和再生提供了一种新途径。骨髓间充质干细胞(BMSCs)具有多向分化潜能,因其取材简单、来源广泛、增殖能力强,无伦理争议,免疫排斥反应小而备受关注。BMSCs在特定区域定向分化成为靶细胞是干细胞治疗的一个重要前提,尤其受到生物材料表面正负电荷、亲疏水和不同的拓扑结构的影响。材料表面涂层蛋白或接枝多肽能够促进BMSCs的分化能力,而生物材料不同的机械性能、几何形状也会影响BMSCs的分化方向。本文综述了近期生物材料调控BMSCs分化的研究结果,为基于BMSCs的组织工程和再生医学材料的设计提供借鉴和指导。