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81.
Hanene Zemmouri Sonda Ammar Amel Boumendjel Mahfoud Messarah Abdelfattah El Feki Mohamed Bouaziz 《Arabian Journal of Chemistry》2019,12(8):1954-1963
The aqueous and hydroalcoholic extracts of borage (Borago officinalis) leaves from Annaba region (Algeria) were preliminary analyzed for their phenolic profile (total phenolics, total flavonoids, total flavonols, total tannins and total anthocyanins). These extracts were evaluated for their antioxidant properties by different methods such as DPPH radical scavenging, test NBT and total antioxidant activity. The two extracts have exhibited a high antiradical capacity. Indeed, the ethanolic extract showed the lower IC50 values and the highest amount of phenolics (94.09 ± 1.72 mg gallic acid/g dry extract). Using LC-MS/MS analysis, it was possible to identify phenolic acids, flavonoids, sterol and for the first time oleuropein was identified in the aqueous extract of the plant. The obtained results have demonstrated that phenolic compounds are the major contributor to the antioxidant activity of plants. 相似文献
82.
基于接触力学理论和线性互补问题的算法, 给出了一种含接触、碰撞以及库伦干摩擦, 同时具有理想定常约束(铰链约束) 和非定常约束(驱动约束) 的平面多刚体系统动力学的建模与数值计算方法. 将系统中的每个物体视为刚体, 但考虑物体接触点的局部变形, 将物体间的法向接触力表示成嵌入量与嵌入速度的非线性函数,其切向摩擦力采用库伦干摩擦模型. 利用摩擦余量和接触点的切向加速度等概念, 给出了摩擦定律的互补关系式; 并利用事件驱动法, 将接触点的黏滞-滑移状态切换的判断及黏滞状态下摩擦力的计算问题转化成线性互补问题的求解. 利用第一类拉格朗日方程和鲍姆加藤约束稳定化方法建立了系统的动力学方程, 由此可降低约束的漂移, 并可求解该系统的运动、法向接触力和切向摩擦力, 还可以求解理想铰链约束力和驱动约束力. 最后以一个类似夯机的平面多刚体系统为例, 分析了其动力学特性, 并说明了相关算法的有效性. 相似文献
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84.
根据热式感应原理,专门设计热式感应传感器,用于测量蒸汽压缩制冷循环中干式蒸发器出口的气液两相流动状态;热式感应传感器的测量数据与蒸发器出口流型、过热度等参数的综合比较分析表明:热式感应传感器可以辨识出蒸发器出口过热蒸汽、雾状流和二者交替三种流动状态.同时,实验数据表明蒸发器出口处于过热蒸汽、雾状流二者交替的过渡区时其换热效率最佳,因此热式感应传感器可以用于作为膨胀阀-干式蒸发器调节回路的反馈信号.应用热式感应传感器对蒸发器出口状态的随机性和周期性波动的测量证明:热式感应传感器动态性能良好,可以实时反映蒸发器出口状态变化. 相似文献
85.
A primitive-variable Riemann method for solution of the shallow water equations with wetting and drying 总被引:1,自引:0,他引:1
P. Sivakumar D.G. Hyams L.K. Taylor W.R. Briley 《Journal of computational physics》2009,228(19):7452-7472
A Riemann flux that uses primitive variables rather than conserved variables is developed for the shallow water equations with nonuniform bathymetry. This primitive-variable flux is both conservative and well behaved at zero depth. The unstructured finite-volume discretization used is suitable for highly nonuniform grids that provide resolution of complex geometries and localized flow structures. A source-term discretization is derived for nonuniform bottom that balances the discrete flux integral both for still water and in dry regions. This primitive-variable formulation is uniformly valid in wet and dry regions with embedded wetting and drying fronts. A fully nonlinear implicit scheme and both nonlinear and time-linearized explicit schemes are developed for the time integration. The implicit scheme is solved by a parallel Newton-iterative algorithm with numerically computed flux Jacobians. A concise treatment of characteristic-variable boundary conditions with source terms is also given. Computed results obtained for the one-dimensional dam break on wet and dry beds and for normal-mode oscillations in a circular parabolic basin are in very close agreement with the analytical solutions. Other results for a forced breaking wave with friction interacting with a sloped bottom demonstrate a complex wave motion with wetting, drying and multiple interacting wave fronts. Finally, a highly nonuniform, coastline-conforming unstructured grid is used to demonstrate an unsteady simulation that models an artificial coastal flooding due to a forced wave entering the Gulf of Mexico. 相似文献
86.
87.
A fed-batch culture system with constant feeding (glucose 80 g L−1, 0.25 ml min−1) was used to study the influence of glucose on cell dry weight and exopolysaccharides production from submerged Tremella fuciformis spores in a 5-L stirred-tank bioreactor. The results showed that high levels of cell mass (9.80 g L−1) and exopolysaccharides production (3.12 g L−1) in fed-batch fermentation were obtained after 1 h of feeding, where the specific growth rate (μ) and exopolysaccharides yield on substrate consumed (YP/S) were 0.267 d−1 and 0.14 g g−1. Unlike batch fermentation, maximal cell mass and exopolysaccharides production merely reached 7.11 and 2.08 g L−1; the specific growth rate (μ) and exopolysaccharides yield on substrate consumed (YP/S) were 0.194 d−1 and 0.093 g g−1, respectively. It is concluded that the synthesis of exopolysaccharides can be promoted effectively when feeding glucose
at a late exponential phase. 相似文献
88.
89.
90.
液相色谱-串联质谱法测定蔬菜和水果中6种新型酰胺类杀菌剂的残留量 总被引:1,自引:0,他引:1
建立了蔬菜、水果中啶酰菌胺、氟啶酰菌胺、环氟菌胺、嘧菌胺、双炔酰菌胺和硅噻菌胺6种新型酰胺类杀菌剂残留量的液相色谱-串联质谱(liquid chromatography-tandem mass spectrometry, LC-MS/MS)检测方法。试样经乙腈提取、Florisil固相萃取柱净化、以乙腈和水为流动相梯度洗脱、结合新型核壳型填料色谱柱(Poroshell 120 EC-C18)分离,采用电喷雾正离子扫描、多反应监测模式质谱检测,外标法定量。结果表明:固相萃取结合新型色谱柱分离解决了酰胺类农药分析中基质效应强的难点问题。6种杀菌剂在0.5~100 μg/L范围内线性关系良好,相关系数(r)≥0.9990;对7种蔬菜及3种水果进行0.5、5和50 μg/kg 3个加标水平的回收试验,回收率为65%~124%,相对标准偏差(RSD, n=5)为1%~18%; 6种杀菌剂的方法检出限(S/N≥3)为0.10~0.17 μg/kg。该净化、分离模式显著降低了蔬菜、水果中6种新型酰胺类农药的基质效应,方法简单准确,可满足蔬菜和水果中啶酰菌胺等6种新型酰胺类杀菌剂残留检测的要求。 相似文献