Development of a liquid chromatography-mass spectrometry method for the determination of ursolic acid in rat plasma and tissue: application to the pharmacokinetic and tissue distribution study

A fast and sensitive liquid chromatography–mass spectrometry method was developed for the determination of ursolic acid (UA) in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate using gradient elution. Quantification was performed by selected ion monitoring with (m/z)⁻ 455 for UA and (m/z)⁻ 469 for the IS. The method was validated in the concentration range of 2.5 − 1470 ng mL⁻¹ for plasma samples and 20 − 11760 ng g⁻¹ for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7% to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 − 106.9% and 82.1 − 108.1%, respectively. Recoveries in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL⁻¹ or 4.0 ng g⁻¹. The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The main pharmacokinetic parameters obtained were T _max = 0.42 ± 0.11 h, C _max = 1.10 ± 0.31 μg mL⁻¹, AUC = 1.45 ± 0.21 μg h mL⁻¹ and K _a = 5.64 ± 1.89 h⁻¹. The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats.     

The cyclicity and period function of a class of quadratic reversible Lotka-Volterra system of genus one

In this paper, we investigate a class of quadratic reversible Lotka-Volterra system of genus one with b=3/5. It is proved that the cyclicity of the period annulus under quadratic perturbations is equal to two. Moreover, we prove that the period function of its period trajectories is monotone increasing.     

Occurrence and estimation of trans-resveratrol in one-year-old canes from seven major Chinese grape producing regions

The concentration of trans-resveratrol in 165 grape cane samples from three major grape production regions and four large distribution centers of Chinese wild Vitis species were determined by reversed-phase high-performance liquid chromatography (HPLC). Among the different genotype groups and purpose of uses, cultivars of V. vinifera had much higher amounts of trans-resveratrol than did the cultivars of both V. labrusca or V. labrusca and V. vinifera hybrids, and within the V. vinifera species, significantly higher amounts of trans-resveratrol were found in wine grapes compared to table ones. No significant differences were observed between V. labrusca and its hybrids from crosses with V. vinifera, and between red cultivars and white ones (P < 0.05 or P < 0.01). The contents of trans-resveratrol, as a normal constituent occurring in grape canes, in Chinese wild species of V. amurensis, V. pentagona, and V. davidii from their native habitats were also relatively high.     

我国固定资产投资对经济发展影响的区域性差异 ——基于省级面板数据

根据我国固定资产投资对经济发展影响区域性差异,以省级面板数据为基础建立回归模型,分析了不同地区的固定资产投资对经济发展作用效果的大小和差异.结果表明,固定资产投资是我国经济发展的主要驱动力,具体而言,固定资产投资对经济发展影响最大的地区是北京和上海,其次是重庆、内蒙古、吉林,再次是四川、西藏以及大部分东部沿海地区,然后是广大的中西部地区,最后是河北、黑龙江、海南以及西北部的一些地区.因此,固定投资效果与经济发展水平存在一定关系.     

最大均方差异统计量的一般界

经典的最大均方差异统计量MMD_b(F,X,Y)和MMD_u²(F,X,Y)基于等量假设(即m=n)来检验两组样本X={x1,x2,……,x_m}和Y={y1,y2,……,y_n}是否来自不同的分布.本文对样本等量假设进行了放松,推广了经典的最大均方差异统计量界,推导出当m≠n时统计量MMD_b(F,X,Y)和MMD_u²(F,X,Y)的一般界.结果表明经典的最大均方差异统计量界是本文推导的最大均方差异统计量一般界的特例.     

Preparations on Several GRIN Lenses

Gradient index materials have been developed from glass melting process to GRIN lenses. Two kinds of GRIN lenses have been fabricated by ion-exchange and glass fusion/diffusion. The main applications to GRIN lenses are demonstrated.     

Studies on novel macrocyclization methods of cembrane-type diterpenoids: a Stille cyclization approach to (±)-isocembrene

An efficient total synthesis of (±)-isocembrene via an intramolecular Stille cross-coupling reaction is described. A novel strategy towards the 1,3-diene-based cembrane-type macrocyclic diterpenoids has been realized.     

光互连中二元计算全息算法的研究

二元计算全息(BCGH)是光学信息处理中一个重要元件,其在动态光互连中被广泛使用.为了更好地在光互连中应用BCGH,本文设计改进了二元计算全息的选代算法,比较了几种内能函数下的迭代算法所设计的BCGH,对其象质的不同指标进行了分析.结果表明,用迭代搜索算法是光互连应用中设计BCGH的一种较理想算法.     

INITIAL VALUE PROBLEMS FOR NONLINEAR DEGENERATE SYSTEMS OF FILTRATION TYPE

In this paper, the periodic boundary problem and the initial value problem for the nonlinear system of parabolic type $\[{u_t} = (grad\varphi (u))\]$ are studied, where $\[u = ({u_1}, \cdots ,{u_N})\]$ is an N-dimensional vector valued function, $\[\varphi (u)\]$ is a strict convex function of vector variable $\[u\]$, and its matrix of derivatives of second order is zero-definite at $\[u = 0\]$. This system is degenerate. The definition of the generalized solution of the problem: $\[u(x,t) \in {L_\infty }((0,T);{L_2}(R)),\]$, grad $\[\varphi (u) \in {L_\infty }((0,T);W_2^{(1)}(R)),\]$ and it satisfies appropriate integral relation. The existence and uniqueness of the generalized solution of the problem are proved. When N=1, the system is the commonly so-called degenerate partial differential equation of filtration type.