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Resistive oxygen sensors based on gallium oxide were fabricated in order to analyze their sensing performances (as sensitivity, response, and recovery time) in an oxygen atmosphere at 1000°C. We prepared three types of sensors using a β‐Ga2O3 single crystal in a sandwich structure with Pt pad electrodes and β‐Ga2O3 polycrystalline thin films deposited by using both the sputtering technique and the chemical solution deposition method. For thin‐film sensors, Pt interdigital electrodes were deposited on the surface of the films using the lift‐off method. X‐ray diffraction and atomic force microscopy investigations were performed to compare the structure and surface morphology of the samples. We achieved a response time of 10 s at 1000°C, while the sensitivity was 1.03 for the single crystal and 1.35–1.45 for thin films. The sensing properties depend on the preparation condition of Ga2O3 devices.

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To investigate the relationship between the tumor growth rate of the primary breast cancer and its prognosis, records for 122 breast cancer patients in 9 hospitals in Japan were retrospectively reviewed. These records contained at least two measurements of the same tumor mass in the breast. So the growth rate was estimated from these measurements taken at different points in time. The doubling time of the breast tumors showed an approximately log‐normal distribution. The geometric mean of doubling times for all cases was 174 days. The solid‐tubular histologic type of carcinoma had the shortest geometric mean of doubling time (126 days), the scirrhous carcinoma had the second shortest one (205 days), and the papillotubular carcinoma had the longest one (252 days). The patients with shorter doubling time of tumor tended to have a poorer prognosis. The Cox multiple regression analysis showed that the tumor growth rate was related significantly with survival, after adjusting for other covariates such as clinical stage, lymph node metastasis, age of patient, histological type, and year of treatment.