Investigation of HIT solar cells low frequency noise characteristics

The effect of solar cell fragment annealing on its noise characteristics is shown. The calculated difference in relaxation times arising from the change in noise after annealing was 30%. Measurements of noise characteristics in the dark and under illumination with a red laser with different radiation power were carried out. Close to linear dependences of noise power reduction with increasing radiation power were obtained.

Caspase-mediated apoptosis of trophoblasts in term human placental villi is restricted to cytotrophoblasts and absent from the multinucleated syncytiotrophoblast

Human placental villi are surfaced by a multinucleated and terminally differentiated epithelium, the syncytiotrophoblast, with a subjacent layer of mononucleated cytotrophoblasts that can divide and fuse to replenish the syncytiotrophoblast. The objectives of this study were i) to develop an approach to definitively identify and distinguish cytotrophoblasts from the syncytiotrophoblast, ii) to unambiguously determine the relative susceptibility of villous cytotrophoblasts and syncytiotrophoblast to constitutive and stress-induced apoptosis mediated by caspases, and iii) to understand the progression of apoptosis in villous trophoblasts. Confocal microscopy with co-staining for E-cadherin and DNA allowed us to clearly distinguish the syncytiotrophoblast from cytotrophoblasts and identified that many cytotrophoblasts are deeply interdigitated into the syncytiotrophoblast. Staining for specific markers of caspase-mediated apoptosis indicate that apoptosis occurs readily in cytotrophoblasts but is remarkably inhibited in the syncytiotrophoblast. To determine if an apoptotic cell or cell fragment was from a cytotrophoblast or syncytiotrophoblast, we found co-staining with E-cadherin along with a marker for apoptosis was essential: in the absence of E-cadherin staining, apoptotic cytotrophoblasts would easily be mistaken as representing localized regions of apoptosis in the syncytiotrophoblast. Regions with perivillous fibrin-containing fibrinoid contain the remnants of trophoblast apoptosis, and we propose this apoptosis occurs only after physical isolation of a region of the syncytium from the main body of the syncytium. We propose models for the progression of apoptosis in villous cytotrophoblasts and for why caspase-mediated apoptosis does not occur within the syncytium of placental villi.

Thymidylate kinase from Acetabularia. I. Properties of the enzyme

The occurrence of a dTMP kinase as well as a dTDP kinase in Acetabularia mediterranea has been demonstrated. A test system was developed by which it was possible to estimate the enzyme activity in an individual Acetabularia cell or even in a cell fragment. The enzyme catalyses the phosphorylation of dTMP in the presence of ATP. In the test system described, dTTP is formed as well as dTDP. This indicates that there is also a dTDP kinase present in the enzyme preparation. Characteristics of the enzyme such as pH optima at pH 7.0 and 8.75, a temperature optimum at 45 degrees C, a Km value of 3.3 X 10(−6) M and a high specificity for ATP were established. In homogenates that were preserved at −70 degrees C the enzyme activity was retained even after many weeks. Freezing at −70 degrees C and then thawing resulted in an increase in enzyme activity. The enzyme was inhibited by low concentrations of dTTP. After centrifugation of homogenates the greater part of the enzyme activity was found in the sediment. From the observation that purified chloroplast preparations contained most of the dTMP kinase activity, and that chlorophyll and enzyme activity cosedimented in a linear sucrose gradient, it was concluded that the enzyme is located in the chloroplasts.