Willis环瞬态血液流体动力特性数值分析

针对左颈内动脉在无狭窄和完全阻塞情况下交通动脉中的血液瞬态流动采用颅内Willis环二维模型进行计算分析.计算得到完整环、交通动脉大脑前动脉缺失情况下各交通动脉血液流量变化趋势.结果表明交通动脉中血液流量变化最大的情况为:右侧大脑前动脉缺失同时左颈内动脉阻塞;在左(右)大脑前动脉近端缺失时前交通动脉中血液流量变化趋势与左(右)大脑前动脉远端相同;左侧后交通动脉在左颈内动脉狭窄比较严重时血液流动方向就会发生改变;在完整环、左颈内动脉阻塞时前交通动脉中的血液流量大于后交通动脉.     

颅内Willis环二维血液动力学计算分析

采用颅内二维Willis环模型,对血管在不同程度狭窄情况下的血液流动进行稳态计算与分析,计算中采用了进出口处的压力边界条件和无滑移固壁条件.计算得到完整环和交通动脉缺失情况下各进出口血管流量变化曲线.所获结果表明,完整Willis环中,前交通动脉的代偿能力在左颈内动脉狭窄率达到25%以后才能得到比较明显的体现;后交通动脉缺失情况下前交通动脉的代偿能力变弱;Willis环的前部和后部有相对独立性,只有在主要进口动脉严重阻塞的时候,单侧的独立性才丧失.     

Optical study on topological superconductor candidate Sr-doped Bi2Se3

Utilizing infrared spectroscopy, we study the charge dynamics of the topological superconductor candidate Sr$_x$Bi$_2$Se$_3$. The frequency-dependent reflectivity $R(\omega$) demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing. The plasma edge shows a slight blue shift upon cooling, similar to the behavior of Cu$_x$Bi$_2$Se$_3$. As the carrier concentration $n$ obtained by Hall resistivity increases slightly with the decreasing temperature, the effective mass is proved to increase as well, which is in contrast with that of Cu$_x$Bi$_2$Se$_3$.We also perform the ultrafast pump-probe study on the Sr$_{0.2}$Bi$_2$Se$_3$ compounds. Resembling its parent compound Bi$_2$Se$_3$, three distinct relaxation processes are found to contribute to the transient reflectivity. However, the deduced relaxation times are quite different. In addition, the electron-optical-phonon coupling constant is identified to be $\lambda = 0.88$.