Hybrid-Trefftz有限元法的研究进展

系统概述了Ｈｙｂｒｉｄ Ｔｒｅｆｆｔｚ有限元法及其在弹性力学中的应用．该单元模型由于在插值函数上的灵活选择性使其比普通有限元能更有效地处理局部效应问题,如孔洞,集中荷载等．通过适当选择单元插值函数可构造出高精度的ｐ－扩展元和一系列满足特殊条件的新单元,以在同等条件下提高计算精度      

2-羟基-3-羧基-5-磺酸基苯基重氮氨基偶氮苯吸光光度法测定微量钯

于pH9.3～10.6Na_2CO_3-NaHCO_3缓冲介质中,在Triton N-101存在下,Pd(Ⅱ)与2-羟基-3-羧基-5-磺酸基苯基重氮氨基偶氮苯(HCSDAA)形成组成比为1:2的红色配合物,其最大吸收波长为530nm,表观摩尔吸光系数为1.05×10~5,线性范围为0～0.7μg·ml~(-1) .结合丁二酮肟螯合,氯仿萃取,方法用于贵金属二次合金中微量钯的测定,相对标准偏差为2.0%(n=6).加标回收率为93.8%～99.3%.     

Determination of senkirkine and senecionine in Tussilago farfara using microwave-assisted extraction and pressurized hot water extraction with liquid chromatography tandem mass spectrometry

Tussilago farfara (Kuan Donghua) is an important Chinese herbal medicine which has been shown to contain many bioactive compounds and widely used to relieve cough and resolve phlegm. However, besides therapeutic bioactive compounds, this herb has been found to contain toxic pyrrolizidine alkaloids (PAs), mainly senkirkine and traces of senecionine. In this report, conditions for microwave-assisted extraction (MAE) and pressurized hot water extraction (PHWE) were optimized for the extraction of the PAs. The results were compared against heating under reflux. It was found that the binary mixture of MeOH:H₂O (1:1) acidified using HCl to pH 2-3 was the optimal solvent for the extraction of the PAs in the plant materials. Liquid chromatography (LC) with ultra-violet (UV) detection and electrospray ionization mass spectrometry (ESI-MS) in the positive mode was used for the determination and quantitation of senkirkine and senecionine in the botanical extract. The proposed extraction methods with LC/MS allow for the rapid detection of the major and the minor alkaloids in T. farfara in the presence of co-eluting peaks. With LC/MS, the quantitative analysis of PAs in the extract was done using internal standard calibration and the precision was found to vary from 0.6% to 5.4% on different days. The limits of detection (LODs) and limits of quantitation (LOQs) for MAE and PHWE were found to vary from 0.26 μg/g to 1.04 μg/g and 1.32 μg/g to 5.29 μg/g, respectively. The method precision of MAE and PHWE were found to vary from 3.7% to 10.4% on different days. The results showed that major and minor alkaloids extracted using MAE and PHWE were comparable to that by heating under reflux. Our data also showed that significant ion suppression was not observed in the analysis of senkirkine and senecionine in the botanical extracts with co-eluting peaks.     

On graphs determining links with maximal number of components via medial construction

Let G be a connected plane graph, D(G) be the corresponding link diagram via medial construction, and μ(D(G)) be the number of components of the link diagram D(G). In this paper, we first provide an elementary proof that μ(D(G))≤n(G)+1, where n(G) is the nullity of G. Then we lay emphasis on the extremal graphs, i.e. the graphs with μ(D(G))=n(G)+1. An algorithm is given firstly to judge whether a graph is extremal or not, then we prove that all extremal graphs can be obtained from K₁ by applying two graph operations repeatedly. We also present a dual characterization of extremal graphs and finally we provide a simple criterion on structures of bridgeless extremal graphs.     

Pressurized hot water extraction of bioactive or marker compounds in botanicals and medicinal plant materials

To reduce the use of organic solvent, pressurized hot water extraction (PHWE) has been shown to be a feasible option for the extraction of bioactive and marker compounds in botanicals and medicinal plants. The parameters that may affect the extraction efficiencies in PHWE include temperature, extraction time and addition of small percentage of organic solvent or surfactants. Currently, applications of PHWE for the extraction of thermally labile compounds in botanicals are still rather limited. PHWE with and without the additional of a small percentage of organic solvent such as ethanol is highly suited for the chemical standardization and quality control of medicinal plants. At the same time, it can be applied at the pilot scale as a manufacturing process for medicinal plants. Surfactant assisted PHWE was found to enhance the extraction of thermally labile and more hydrophobic species in medicinal plants at a lower temperature. The addition of small amount of surfactants in PHWE is highly suited for the determination of bioactive or marker compounds in medicinal plants. With proper optimization, PHWE was observed to have good extraction efficiency and precision when compared to other reference methods of extraction.     

Irregular elliptical plasmonic rings for engineering near-field and phase

Metallic glasses find wide applications in nanotechnology and micro electro-mechanical systems because of their unique physical properties due to their amorphous structures. The material removal mechanism in nanometric cutting of Cu₅₀Zr₅₀, a typical metallic glass, is studied using molecular dynamics method. The chip formation, workpiece deformation and scratching forces under various scratching depths, scratching velocities and temperatures are investigated. The effect of void defect on the cutting behaviors of metallic glass is also explored. The results show that the material removal in nanometric cutting process is based on extrusion instead of shearing, achieving a good understanding of material removal at the nanoscale.