No abstract

Cytoskeleton inhibitors were used to study morphogenesis in the pathogenic and dimorphic fungus Candida albicans. Nocodazole is a specific microtubule inhibitor and chloropropham (CIPC), at high concentrations, is an inhibitor of microtubules and microfilaments. Distribution of microtubules and microfilaments was studied by immunofluorescence techniques using anti-tubulin antibody with FITC-conjugated secondary antibody, and by staining with Rh-phalloidin. Nocodazole did not arrest apical cell elongation at a concentration (20 pg ml-l) that inhibited nuclear division and migration. Cytoplasmic and nuclear microtubules disappeared within 30min in filamentous cells under these conditions. However, the Rh-phalloidin-stained actin granules which were localized in the tips of filamentous cells, and the microfilaments, were arranged normally at this concentration of nocodazole. Growth, and normal distribution of microtubules and microfilaments, were inhibited by a high concentration (200 pg ml-l) of CIPC. At a concentration (100 pg ml-l) of CIPC that permitted nuclear division, apical cell elongation was arrested, and filamentous growth was converted into yeast growth. At this concentration of CIPC, microtubules were distributed normally in filamentous cells. Long microfilaments were not observed, and actin granules did not localize in the tips of filamentous cells, but were distributed throughout the cytoplasmic cortex. Our results show that cytoplasmic microtubules are not essential for the elongation of filamentous cell tips but that microf~laments are apparently essential for this process.

Conduction measurements with simultaneous observations by transmission electron microscopy (TEM) were performed on a thin NiO film, which is a candidate material for resistance random access memories (ReRAMs). To conduct nanoscale experiments, a piezo-controlled TEM holder was used, where a fixed NiO sample and a movable Pt-Ir counter electrode were placed. After the counter electrode was moved to make contact with NiO, I-V measurements were carried out from any selected nanoregions. By applying a voltage of 2 V, the insulating NiO film was converted to a low resistance film. This phenomenon may be the "forming process" required to initialize ReRAMs. The corresponding TEM image indicated a structural change in the NiO layer generating a conductive bridge with a width of 30-40 nm. This finding supports the "breakdown" type forming in the so-called "filament model" of operation by ReRAMs. The inhomogeneity of resistance in the NiO film was also investigated.

We succeeded to observe the "conduction spot" (CS) in the capacitor structure ReRAM, which includes a conductive filament. In this study, we used NiO prepared by thermal oxidation at high temperature as 800°C. It requires a forming process by extra high voltage, which partly removes the top electrode from the resistance switched area.These experiments enabled us to observe the conductive filament directly in CS on NiO ReRAM by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM images, CSs seem to be produced by some kind of breakdown, but we confirmed the reproducible resistance switching at least 50 cycles after the CS generation. By means of energy dispersive X-ray spectroscopy (EDX) with TEM observations, drastic oxygen reduction was recognized in local area within CS of NiO films. Moreover, the CS area depended on the injection power for forming. These experimental data suggest that miniaturization of ReRAM will be achieved by reducing the injection power for forming. *

No abstract

Resistive random access memory (ReRAM) properties in which the resistance of the insulating material drastically changes by voltage application have recently attracted much attention. In this work, molybdenum oxide prepared by thermal oxidation of Mo films was studied to investigate its potential as a material exhibiting ReRAM switching. The samples oxidized between 400 and 600 o C were composed of MoO 3 and were switchable. Current-to-voltage curves, which were measured in air at room temperature by using a Pt-Ir probe as the top electrode, indicated the yielding of both the monopolar and bipolar switching properties. The resistance on-off ratio was between 10 and 10 2 .

Yeast cells of Candida albicans produced germ tubes in a salt-glucose medium containing 4% calf serum a t pH 7 and 37 "C. Hyphal growth continued for 24 h and the filaments did not revert to yeast cells. When cells were grown at pH 4 8 reversion to yeast growth was Observed, despite the presence of serum. The elongation of hyphae was inhibited within 30 min. The distribution of microtubules and microfilaments during pH-regulated morphological transition was studied by an immunofluorescence technique using an antitubulin antibody with a FITC-conjugated secondary antibody, and b y staining with tetramethylrhodaminyl phalloidin for filamentous actin and actin granules. After changing to acidic conditions, microtubules were distributed normally in the cytoplasm; however, microf ilaments disappeared from hyphal cells, and actin granules were localized a t the site of budding. These results show that microf ilaments play an important role during pH-regulated morphological transition.

The resistive switching of NiO sandwiched between Pt bottom and top electrodes are formed by thermal oxidation at the temperature from 300°C to 800°C. The ReRAM characteristics are investigated from the view point of practical applications. The stable and uniform formation of NiO films are revealed by XPS analysis and the chemical compositions of NiO are almost independent of oxidation temperatures. However, the forming voltages of the film prepared at higher oxidation temperature are scattered and reach to high values. This fact indicates that the forming process occurs at the weak spot, and the density of the weak spot is low in the film formed at higher temperature. As a result, the NiO prepared at lower temperature shows stable and lower forming voltages.