Building topological device through emerging robust helical surface states

We propose a nonlocal manipulation method to build topological devices through emerging robust helical surface states in Z_2=0 topological systems. Specifically, in a ribbon of Z_2=0 Bernevig- Hughes-Zhang (BHZ) model with finite-size effect, if magnetic impurities are doped on the top (bottom) edge, the edge states on the bottom (top) edge can be altered according to the strengths and directions of these magnetic impurities. Consequently, the backscattering between the emerging robust helical edge states and gapped normal edge states due to finite-size confinement is also changed, which makes the system alternate between a perfect one-channel conductor and a perfect insulator. This effect allows us to fabricate topological devices with high on-off ratio. Moreover, it can also be generalized to 3D model and more realistic Cd3As2 type Dirac semimetals.Comment: 7 pages, 6 figure

One-dimensional quantum channel in a graphene line defect

Using a tight-binding model, we study a line defect in graphene where a bulk energy gap is opened by sublattice symmetry breaking. It is found that sublattice symmetry breaking may induce many configurations that correspond to different band spectra. In particular, a gapless state is observed for a configuration which hold a mirror symmetry with respect to the line defect. We find that this gapless state originates from the line defect and is independent of the width of the graphene ribbon, the location of the line defect, and the potentials in the edges of the ribbon. In particular, the gapless state can be controlled by the gate voltage embedded below the line defect. Finally, this result is supported with conductance calculations. This study shows how a quantum channel could be constructed using a line defect, and how the quantum channel can be controlled by tuning the gate voltage embedded below the line defect.Comment: 8 pages, 10 figure

Prognosis and related risk factors of patients with scarred uterus complicated with central placenta previa

Objectives: To analyze the prognosis and related risk factors of patients with scarred uterus complicated with central placenta previa.  Material and methods: A total of 272 parturient women admitted to our hospital between June 2013 and December 2016 were selected, of whom 142 cases with central placenta previa were designated as a control group and another 130 with scarred uterus complicated with central placenta previa were allocated as an observation group. The delivery outcomes of the two groups were compared, and the influencing factors were comprehensively analyzed.  Results: The prenatal and postpartum blood losses of the observation group were significantly higher than those of the control group (P < 0.05). The incidence rates of placental adhesion, placenta accreta, hysterectomy and puerperal infection in the obstetric group significantly exceeded those of the control group (P < 0.05). Logistic regression analysis showed that postpartum hemorrhage and placenta implantation were risk factors affecting prognosis (P < 0.05).  Conclusions: Patients with scarred uterus and central placenta previa suffered from serious complications such as profuse postpartum hemorrhage and placental adhesion after delivery. Particular attention should be paid to women with scarred uterus during subsequent pregnancy to prevent placenta previa and to reduce the risks of delivery, thereby benefiting prognosis evaluation.