RESUMO
We explored in-gap states (IGSs) in perovskite oxide heterojunction films. We report that IGSs in these films play a crucial role in determining the formation and properties of interfacial two-dimensional electron gas (2DEG). We report that electron trapping by IGSs opposes charge transfer from the film to the interface. The IGS in films yielded insulating interfaces with polar discontinuity and explained low interface carrier density of conducting interfaces. An ion trapping model was proposed to explain the physics of the IGSs and some experimental findings, such as the unexpected formation of 2DEG at the initially insulating LaCrO3/SrTiO3 interface and the influence of substitution layers on 2DEG.
RESUMO
OBJECTIVE: To evaluate the effect of serum/cerebrospinal fluid (CSF) ratio of human chorionic gonadotropin (hCG) in detecting brain metastases of gestational trophoblast tumor and the significance of prophylactic intrathecal therapy. METHODS: Clinical information of 44 patients with brain metastases (stage IV) and 29 patients with lung metastases (stage III) of gestational trophoblast tumor who were admitted to our hospital between 1986 to 2001 were retrospectively analyzed by case control study. The variability of the ratio and the relationship between brain metastases was investigated, together with the effect of prophylactic intrathecal therapy. RESULTS: Serum/CSF hCG ratio in patients with brain metastases declined with time. The ratio before chemotherapy was in relevant with the size of the lesion which were less than 60 in advanced stages and more than 60 in early stages. Patients of stage III with prophylactic intrathecal therapy did not progress to stage IV. CONCLUSIONS: Serum/CSF hCG ratio before chemotherapy could reflect the encephalic tumor load which had reference value in diagnosis and prognosis and prophylactic intrathecal therapy played an important role in preventing brain metastasis.