白簕果实中总黄酮的测定

为确定白簕果实总黄酮的含量,采用超声辅助法提取白簕果实中的黄酮类化合物,以芦丁为对照,采用分光光度法在510nm处测定白簕果实中的总黄酮.回归方程为:A=1.0471C-0.0012,相关系数r=0.9997,精密度实验RSD为1.653％,稳定性实验(40min)RSD分别为2.011％(芦丁)和1.967％(白簕),平均加标回收率为101％,RSD=1.961％(n=6).采用分光光度法,操作简便,结果准确,灵敏度高,重复性好,准确测定白簕果实中总黄酮含量为76.93mg/g.     

Non-Stoichiometry Effects on the Extreme Magnetoresistance in Weyl Semimetal WTe_2

Non-stoichiometry effect on the extreme magnetoresistance is systematically investigated for the Weyl semimetal WTe_2. Magnetoresistance and Hall resistivity are measured for the as-grown samples with a slight difference in Te vacancies and the annealed samples with increased Te vacancies. The fits to a two-band model show that the magnetoresistance is strongly dependent on the residual resistivity ratio(i.e., the degree of non-stoichiometry),which is eventually understood in terms of electron doping that not only breaks the balance between electron-type and hole-type carrier densities, but also reduces the average carrier mobility. Thus the compensation effect and ultrahigh mobility are probably the main driving force of the extreme magnetoresistance in WTe_2.     

新型hollandite结构化合物BiIr_4Se_8单晶的生长,结构与基本物性研究（英文）

通过助溶剂法制得新型单晶BiIr_4Se_8.能量色散X射线谱确定样品元素比例约为Bi:Ir:Se≈1:4:8.利用粉末与单晶X射线衍射技术确定了单晶属于单斜晶系,具有扭曲的hollandite结构,其中的一维通道被Bi原子占据.300K以下的电阻与磁化率测试表明,样品属于半导体,且表现抗磁性.Bi在一维通道的无序暗示该材料是一种潜在的热电材料.这种结构容易受掺杂与压力的影响,为进一步探索5d过渡金属化合物中复杂的物理现象提供了良好的平台.