Formation of Si nanocrystallites observed by in situ transmission electron microscopy and their effect on the enhancement of Er photoluminescence in Er-doped SiO2

The formation of Si nanocrystallites (nc-Si) in erbium (Er)-dispersed SiOx (x<=2) films was investigated by in situ annealing while performing transmission electron microscopy measurements. The correlation between the formation of nc-Si and Er ion emissions was also comprehensively investigated by photoluminescence and electron spin resonance measurements. The results showed that the formation of nano-Si region with the suitable size is important for enhancement of Er ion emission

Codoping of boron and phosphorus in silicon nanowires synthesized by laser ablation

Codoping of boron (B) and phosphorus (P) atoms was performed during the synthesis of silicon nanowires (SiNWs) by laser ablation. The observation of a local vibrational mode of B clearly showed B doping in codoped SiNWs, while Fano broadening due to heavy B doping disappeared, indicating compensation by P donors. The electrospin resonance signal of conduction electrons also disappeared due to compensation by B acceptors. These results indicate that codoping of B and P atoms was achieved in SiNWs during laser ablation

Genetic Characterization of Conserved Charged Residues in the Bacterial Flagellar Type III Export Protein FlhA

For assembly of the bacterial flagellum, most of flagellar proteins are transported to the distal end of the flagellum by the flagellar type III protein export apparatus powered by proton motive force (PMF) across the cytoplasmic membrane. FlhA is an integral membrane protein of the export apparatus and is involved in an early stage of the export process along with three soluble proteins, FliH, FliI, and FliJ, but the energy coupling mechanism remains unknown. Here, we carried out site-directed mutagenesis of eight, highly conserved charged residues in putative juxta- and trans-membrane helices of FlhA. Only Asp-208 was an essential acidic residue. Most of the FlhA substitutions were tolerated, but resulted in loss-of-function in the ΔfliH-fliI mutant background, even with the second-site flhB(P28T) mutation that increases the probability of flagellar protein export in the absence of FliH and FliI. The addition of FliH and FliI allowed the D45A, R85A, R94K and R270A mutant proteins to work even in the presence of the flhB(P28T) mutation. Suppressor analysis of a flhA(K203W) mutation showed an interaction between FlhA and FliR. Taken all together, we suggest that Asp-208 is directly involved in PMF-driven protein export and that the cooperative interactions of FlhA with FlhB, FliH, FliI, and FliR drive the translocation of export substrate

Effects of oxygen concentration on the proliferation and differentiation of mouse neural stem cells in vitro.

BACKGROUND AND PURPOSE: Cerebral ischemia is known to elicit the activation of neural stem cells (NSCs); however its mechanism is not fully determined. Although oxygen concentration is known to mediate many ischemic actions, there has been little attention given to the role of pathological oxygen changes under cerebral ischemia on the activation of NSCs. We investigated the effects of various oxygen concentrations on mouse neural stem cells in vitro. METHODS: NSCs were cultured from the ganglionic eminence of fetal ICR mice on embryonic day 15.5 using a neurosphere method. The effects of oxygen concentrations on proliferation, differentiation, and cell death of NSCs were evaluated by bromodeoxyuridine (BrdU) incorporation, immunocytochemistry, and TUNEL assay, respectively. RESULTS: The highest proliferation and the neuronal differentiation of the NSCs were observed in 2% oxygen, which yielded significantly higher proportions of both BrdU-labeled cells and Tuj1-positive cells when compared with 20% and 4% oxygen. On the other hand, the differentiation to the astrocytes was not affected by oxygen concentrations, except in the case of anoxia (0% oxygen). The cell death of the NSCs increased in lower oxygen conditions and peaked at anoxia. Furthermore, the switching of the neuronal subtype differentiation from GABA-positive to glutamate-positive neurons was observed in lower oxygen conditions. CONCLUSIONS: These findings raise the possibility that reduced oxygen levels occurring with cerebral ischemia enhance NSC proliferation and neural differentiation, and that mild hypoxia (2% oxygen), which is known to occur in the ischemic penumbra, is suitable for abundant neuronal differentiation