Evolutionary mechanism of safety performance for spur gear pair based on meshing safety domain

Nonlinear Dynamics - Micro-vibrations in satellites mainly originate from the control moment gyroscope because of its mass imbalance, which seriously affect the image accuracy of high-resolution...     

Highly enantioselective cyanation of aldehydes catalyzed by a multicomponent titanium complex

A new multicomponent bifunctional catalytic system based on a titanium complex was used for the efficient enantioselective cyanation of aldehydes. The catalyst was readily prepared from tetraisopropyl titanate (Ti(Oi-Pr)4), (S)-6,6'-dibromo-1,1'-bi-2-naphthol (1e), cinchonine (2a), and (1R,2S)-(-)-N-methylephedrine (3b). It was revealed that the combination of 1e, 2a, 3b, and Ti(IV) was essential in this cyanation. The reaction proceeded smoothly in the presence of a catalytic amount of the multicomponent catalyst to afford the desired cyanohydrins ethyl carbonates in moderate to excellent isolated yields (up to 95%) with high enantioselectivities (up to 94% ee). A catalytic cycle based on experimental phenomena was proposed to explain the origin of the asymmetric induction.     

Exponential mixing for the Teichmüller flow

We study the dynamics of the Teichmüller flow in the moduli space of Abelian differentials (and more generally, its restriction to any connected component of a stratum). We show that the (Masur-Veech) absolutely continuous invariant probability measure is exponentially mixing for the class of Hölder observables. A geometric consequence is that the $SL(2,\mathbb{R})We study the dynamics of the Teichmüller flow in the moduli space of Abelian differentials (and more generally, its restriction to any connected component of a stratum). We show that the (Masur-Veech) absolutely continuous invariant probability measure is exponentially mixing for the class of H?lder observables. A geometric consequence is that the action in the moduli space has a spectral gap.     

Effects of the Auxiliary Ligands on the Structures of Diphenate Complexes: From 1D Helical Chain to 2D Network

Two coordination polymers, [Cd(dpa)(L1)] ( 1 ) and [Cd(dpa)(L2)]·CH₃CH₂OH₃ ( 2 ) (L1 = 2,6‐bis(1H‐benzimidazol‐2yl)‐pyridine, L2 = 2,2′‐(1,4‐butanediyl) bis (1H‐ benzimidazole) (L2), both of which contain helical chain subunits, were synthesized by the reaction of Cd^II salts and diphenic acid (H₂dpa) with rigid, chelating and flexible, bridging auxiliary ligands, respectively. Compound 1 has a 1D helical chain structure, in which dpa^2– as bridging ligand is responsible for the formation of the main framework and L1 as chelating ligand grafts on one side of the helical chain. This structure is further extended into a 3D supramolecular framework through two kinds of strong hydrogen bonding interactions. Compound 2 has a 2D structure, in which dpa^2– bridges the Cd^II atoms into helical chains and L2 bridges the left‐ and right‐handed chains into a racemic layer with a [4,4] topology.     

Characterization of catechol 1,2-dioxygenase from cell extracts of <Emphasis Type="Italic">Sphingomonas xenophaga</Emphasis> QYY

Sphingomonas xenophaga QYY, capable of growing significantly on more than ten kinds of aromatic compounds as sole carbon source, was used to study characterization of catechol 1,2-dioxygenase (C12O) in cell extracts. Characterization of the crude C12O showed that the maximum activity was obtained at 40–70°C and pH 7.8–8.8. Metal ions had different influences on the activity of crude C12O. It was suggested that strain QYY possessed an inducible and ferric-dependent C12O. Kinetic studies showed that the value of V _max and K _m was 0.25 μmol catechol/L/mg protein/min and 52.85 μmol/L, respectively. In addition, the partial purification of C12O was achieved by a HiTrap Q Sepharose column chromatography. Supported by the National Natural Science Foundation of China (Grant No. 50608011) and the 39th Postdoctoral Funds of China (Grant No. 20060390983)     

氢化物发生-原子荧光光谱法测定植物样品中的硒

建立了氢化物发生-原子荧光光谱法测定植物样品中硒的分析方法。研究了试剂及预还原方式对硒原子荧光强度的影响,探讨了共存离子对硒测定的影响和消除方法。在最佳消解条件和测定条件下,硒的线性回归方程为I=139.98c+27.71,线性范围为0～10ng.mL-1,相关系数为1.000 0,检出限为1.45ng.g-1。测定标准物质中硒的回收率为98.9%～101%,其平均值为100%。对灌木枝叶样品中的硒进行分析,其相对标准偏差为0.73%(n=9)。以国家标准物质(GSV-1)为监控样品,测定值与标准值吻合。该方法具有成本低、操作简单和高效分析的优点,并成功用于植物样品中硒的测定。     

基于T-S双线性模型的不确定离散时滞非线性系统的分段广义H2控制

针对系统中普遍存在时滞和系统不确定性现象,基于分段二次李雅普诺夫函数稳定性理论,讨论一类受干扰的不确定离散时滞模糊双线性系统的广义H2稳定控制问题。通过设计非脆弱分段状态反馈控制器,使闭环系统在允许参数不确定范围内广义H2稳定,控制器的设计可以通过序列线性规划矩阵方法(SLPMM sequential linear programming matrix method)方法求解得到。仿真例子验证了该方法的有效性。     

Optimal Concentration Inequalities for Dynamical Systems

For dynamical systems modeled by a Young tower with exponential tails, we prove an exponential concentration inequality for all separately Lipschitz observables of n variables. When tails are polynomial, we prove polynomial concentration inequalities. Those inequalities are optimal. We give some applications of such inequalities to specific systems and specific observables.     

压缩双裂纹和单裂纹圆孔板应力强度因子公式

从理论模型和数值分析上澄清了国外文献关于压缩双裂纹圆孔板(double cleavage drilled compression,DCDC) 的应力强度因子不同的公式引起的混淆. 证明Plaisted 等用修正压缩无限大板中圆孔双边裂纹的解和欧拉-伯努利梁理论得到的DCDC 应力强度因子公式都存在推导和原理性的失误. 指出Jenne 等推导的公式形式过于复杂不便使用, 而He 等的公式适用范围偏小. 通过拟合有限元法宽范围数值计算结果导出DCDC 的应力强度因子的新公式, 该公式形式简单, 对无量纲裂纹长度和无量纲板宽度适用范围较大, 最大误差是7%. 此外, 还对新提出的压缩单裂纹圆孔板(single cleavage drilled compression, SCDC)做了分析, 首次得到的SCDC应力强度因子公式的最大误差是5%. 给出的2 个公式可分别用于脆性材料DCDC 或SCDC 试样的断裂韧度测试.     

Oxidative Stress and Antioxidative Therapy in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is clinically characterized by a progressive increase in pulmonary artery pressure, followed by right ventricular hypertrophy and subsequently right heart failure. The underlying mechanism of PAH includes endothelial dysfunction and intimal smooth muscle proliferation. Numerous studies have shown that oxidative stress is critical in the pathophysiology of PAH and involves changes in reactive oxygen species (ROS), reactive nitrogen (RNS), and nitric oxide (NO) signaling pathways. Disrupted ROS and NO signaling pathways cause the proliferation of pulmonary arterial endothelial cells (PAECs) and pulmonary vascular smooth muscle cells (PASMCs), resulting in DNA damage, metabolic abnormalities, and vascular remodeling. Antioxidant treatment has become a main area of research for the treatment of PAH. This review mainly introduces oxidative stress in the pathogenesis of PAH and antioxidative therapies and explains why targeting oxidative stress is a valid strategy for PAH treatment.