Investigation on the origin of wurtzite domains in thick cubic GaN using reactive ion etching

We measured the depth profiling of photoluminescence (PL) in cubic GaN films. The depth-resolved PL of normal grown GaN layers showed that the near-band-edge luminescence intensities of both cubic and wurtzite domains remained constant only until an etching depth of up to 2.7 mu m, but their ratio remained unchanged at all etching depths. Moreover, when a thin In0.1Ga0.9N layer was sandwiched between two GaN layers, the content of the wurtzite domains increased, and its distribution showed a dependence on thickness. As the reactive ion etching depth increased, the PL intensity ratio of cubic GaN to wurtzite domains increased. Based on the distribution, the strain relaxation, instead of the instability of cubic GaN at high temperature, was attributed to the origin of wurtzite domains. (C) 2000 Elsevier Science S.A. All rights reserved.

NADPH oxidase-mediated generation of reactive oxygen species: A new mechanism for X-ray-induced HeLa cell death

Oxidative damage is an important mechanism in X-ray-induced cell death. Radiolysis of water molecules is a source of reactive oxygen species (ROS) that contribute to X-ray-induced cell death. In this study, we showed by ROS detection and a cell survival assay that NADPH oxidase has a very important role in X-ray-induced cell death. Under X-ray irradiation, the upregulation of the expression of NADPH oxidase membrane Subunit gp91(phox) was dose-dependent. Meanwhile, the cytoplasmic subunit p47(phox) was translocated to the cell membrane and localized with p22(phox) and gp91(phox) to form reactive NADPH oxidase. Our data Suggest, for the first time, that NADPH oxidase-mediated generation of ROS is an important contributor to X-ray-induced cell death. This suggests a new target for combined gene transfer and radiotherapy.

Structural and photoluminescent properties of ZnO films deposited by radio frequency reactive sputtering

Zinc oxide films with c-axis preferred orientation were deposited on silicon (100) substrates by radio frequency (RF) reactive sputtering. The properties of the samples were characterized by X-ray diffractometer, X-ray photoelectron spectroscopy and fluorescent-spectrophotometer. The effect of sputtering power and substrate temperature on the structural and photoluminescent (PL) properties of the ZnO films was investigated. The results indicated that when the sputtering power is 100 W and the substrate temperature is 300-400 degrees C, it is suitable for the growth of high c-axis orientation and small strain ZnO films. A violet peak at about 380 nm and a blue band at about 430 nm were observed in the room temperature photoluminescence spectra, and the origin of blue emission was investigated.

Stress Resistance and Disease Resistance in Seaweeds:The Role of Reactive Oxygen Metabolism

It has become clear that the last 15-20 years that the immediate effect of a wide range of environmental stresses,and of infection,on vascular plants is to increase the information of reactive oxygen species(ROS) and to impose oxidative stress on the cells.Since 1994,sufficient examples similar responses in a broad range of marine macroalgae have been decribed to show that reactive oxygen metabolism also underlies the mechanisms by which seaweeds respond(and become resistant) to stress and infection.Desiccation,freezing,low temperatures,high light,ultraviolet radiation,and heavy metals all tend to result in a gradual and continued buildup of ROS because photosynthesis is inhibited and excess energy results in the formation of singlet oxygen.The response to other stresses (infection or oligosaccharides which signal that infection is occurring,mechanical stress,hyperosmotic shock) is quite different-a more rapid and intence,but short-lived production of ROS ,discribed as an "oxidative burst"-which is attributed to activation of NADPHoxidases in the plasma membrane.Seaweed species that are able to survive such stresses or resist infection have the capacity to remove the ROS through a high cellular content of antioxidant compounds,or a high activity of antioxidant enzymes.

Numerical Simulation of Reactive Extrusion Processes for Activated Anionic Polymerization

In order to deal with the complicated relationships among the variables of the reactive extrusion process for activated anionic polymerization, a three-dimensional equivalent model of closely intermeshing co-rotating twin screw extruders was established. Then the numerical computation expressions of the monomer concentration, the monomer conversion, the average molecular weight and the fluid viscosity were deduced, and the numerical simulation of the reactive extrusion process of Styrene was carried out. At last, our simulated results were compared with Michaeli's simulated results and experimental results. (C) 2007 Elsevier B.V. All rights reserved

Preparation and properties of polyether pentaerythritol mono-maleate grafted linear low density polyethylene by reactive extrusion

A reactive type nonionic surfactant, polyether pentaerythritol mono-maleate (PPMM) was synthesized in our laboratory. PPMM was adopted as functionalizing monomer and grafted onto linear low density polyethylene (LLDPE) with a melt reactive extrusion procedure. FT-IR was used to characterize the formation of grafting copolymer and evaluate their degree of grafting. The effects of monomer concentration, reaction temperature and screw run speed on the degree of grafting were studied systematically. Isothermal crystallization kinetics of LLDPE and LLDPE-g-PPMM samples was carried out using DSC.