Fumiko Nakazawa

Annealing of γ-ray irradiated N-type germanium

Abstract Isochronal and isothermal annealing above room temperature has been studied in antimony and arsenic doped γ-irradiated germanium. Three annealing stages are found at 370, 430 and 530°K with activation energies of 0·7–0·8 eV, 1·2–1·3 eV and 2·2 (As-doped)–2·5 (Sb-doped) eV, respectively. Impurity dependence of annealing behavior is found in all these stages. The results are discussed in terms of electronic and elastic interactions of defect centers with impurity atoms.

Induction of early decidualization by cadmium, a major contaminant of cigarette smoke

To investigate the effect of cadmium (Cd) contamination on endometrial function, human endometrial stromal cells were isolated and cultured with E(2) plus P in the presence of Cd, a major contaminant in cigarette smoke, and assayed for PRL concentrations and its messenger RNA expression. Cd significantly increased PRL concentrations in the culture media and significantly up-regulated PRL messenger RNA expression of the endometrial stromal cells, suggesting that Cd stimulates decidualization of the endometrium and may disrupt endometrial environment, causing early decidualization.

Thermally Induced Acceptor Centers in Germanium

In crystals with a very small dislocation density such as in germanium, a long time is necessary to obtain an equilibrium concentration of Schottky-type defects. This is verified by successive-quenching experiments. Analysis of the equilibration process of acceptor centers in n-type germanium at high temperatures gives the activation energy of about 2.0 eV. The formation energy of the thermally induced acceptors is found to be roughly 2 eV from the saturation values of the introduction curves of acceptors. Preliminary results of annealing of thermal acceptors are also described. The results are discussed in terms of vacancies thermally induced into the crystal.

Low Temperature Photoconductivity of F Center in KCl

Transient Photoconductivity of additively colored KCl is studied for excitation in the F , K , L 1 and L 2 bands at low temperatures down to 1.3°K. Electron quantum yield is found near unity in L bands and in high energy tail of K band in the whole temperature range. K band can be divided into two components; K 1 band with low electron yield and K 2 band with unit yield. It is concluded K 2 band corresponds to transition to the conduction band minimum and L bands to the states in the conduction band. Electron yield for K 1 and F bands is studied as a function of temperature and applied electric field. Thermal binding energy of excited state is found the same for K 1 and F states. Field ionization from K 1 state starts at far lower field than from F state. Transport of electrons at low temperature is characterized by non-ohmic behavior above critical field, where electron Schubweg is proportional to E 0.5∼0.7 . The high field behavior can be understood as hot electron phenomena.

Inhibition of proteases involved in embryo implantation by cholesterol sulfate

BACKGROUND Matrix metalloproteinases (MMPs) and the plasminogen activator (PA)/plasmin system are two major groups of proteases involved in the matrix degradation required for embryo implantation. We previously showed that the content of cholesterol sulfate (CS) in rabbit endometrium increases characteristically during the implantation period. Furthermore, CS has been reported to inhibit serine proteases. In this study, we investigated whether CS can regulate the activity of proteases in cultured human endometrial stromal cells. METHODS AND RESULTS CS (1-30 microM) and plasminogen (precursor of plasmin) were added to the culture media of human endometrial stromal cells and incubated for 24 h. Culture media were collected for analysis of plasmin and MMP-2, -3 and -9 enzyme activities using fluorescence assays. Plasmin and MMP-3 activities were significantly reduced by CS in a dose-dependent manner (P < 0.001). Western blot analysis of the culture media revealed that CS inhibited the conversion by plasmin of MMP-3 from the precursor form to the active form. Fluorescence assay using a common substrate of MMP-2 and MMP-9 showed that enzymatic activity remains at approximately 50%, even at 30 microM CS. Gelatin zymography demonstrated that CS inhibited the activation of MMP-9 but not MMP-2 from the precursor, suggesting that the activation of MMP-2 may be independent of plasmin. CONCLUSIONS CS inhibits not only plasmin activity but also MMP activities indirectly by inhibiting the plasmin-mediated process. These findings suggest that CS may be an important regulator of proteolysis during trophoblast invasion.

Impurities dependence of annealing of γ-Ray irradiated n-type germanium

γ-irradiated n-type germanium doped with neutral impurities such as tin and silicon, together with charged impurities such as antimony and arsenic, has been studied by means of isochronal and isothermal annealings. In antimony + tin doped germanium two shallow levels are introduced by γ-ray irradiation. They are situated at 0.14 eV and 0.20 eV below the conduction band and they anneal in different temperature ranges. In antimony doped germanium a shallow level situated at 0.21 eV below the conduction band is introduced by irradiation and its position changes to 0.25 eV after moderate annealing. Both in arsenic doped and arsenic + silicon doped germanium also, a shallow level is introduced by irradiation and its position is obtained to be 0.25 eV after moderate annealing. Discriminative analyses of temperature dependences of Hall coefficients after successive annealings enable us to separate the annealing of shallow levels from that of deep levels. Separated annealing curves show annealing behaviors of defects more clearly. Each annealing stage is discussed in terms of these separated annealing curves.

Low Temperature Hall Mobility and Magnetoresistance in KCl at High Electric Field

Hall mobility of photoelectrons in zone refined and additively colored KCl single crystals is found to be so high as 2×10 4 cm 2 /volt·sec at 4.2°K and to decrease in proportion to E -0.5 beyond a critical electric field. Corresponding to the mobility decrease, photocurrent is proportional to E 0.5 beyond the critical field. Dominant scattering centers at low electric field are concluded to be charged impurities rather than F centers by measurements of Hall effect and magnetoresistance. Polaron transport in KCl crystal is interpreted fairly well by the usual transport theory including hot electron theory. However, two important difficulties become noticeable in applying the usual theory. First, the trapping lifetime of electron is shorter than the scattering time. Secondly, photocurrent saturation is not observed even under very high electric field at which drift velocity of electron is much higher than the thermal velocity and emission of optical phonon is expected to occur appreciably.