Modeling tungsten response under helium plasma irradiation: a review

Tungsten, a leading candidate for plasma-facing materials (PFM) in future fusion devices, will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions. In the past two decades, experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering, thermal and other properties of tungsten, posing a serious danger to the performance and lifetime of tungsten and the steady-state operation of plasma. In this article, we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles, surface morphology, and property changes of tungsten exposed to low-energy helium plasma. The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.     

Cleaning of nitrogen-containing carbon contamination by atmospheric pressure plasma jet

Atmospheric pressure plasma jet (APPJ) was used to clean nitrogen-containing carbon films (C–N) fabricated by plasma-assisted chemical vapor deposition method employing the plasma surface interaction linear device at Sichuan University (SCU-PSI). The properties of the contaminated films on the surface of pristine and He-plasma pre-irradiated tungsten matrix, such as morphology, crystalline structure, element composition and chemical structure were characterized by scanning electron microscopy, grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. The experimental results revealed that the removal of C–N film with a thickness of tens of microns can be realized through APPJ cleaning regardless of the morphology of the substrates. Similar removal rates of 16.82 and 13.78 μm min−1 were obtained for C–N films deposited on a smooth pristine W surface and rough fuzz-covered W surface, respectively. This is a remarkable improvement in comparison to the traditional cleaning method. However, slight surface oxidation was found after APPJ cleaning, but the degree of oxidation was acceptable with an oxidation depth increase of only 3.15 nm. Optical emission spectroscopy analysis and mass spectrometry analysis showed that C–N contamination was mainly removed through chemical reaction with reactive oxygen species during APPJ treatment using air as the working gas. These results make APPJ cleaning a potentially effective method for the rapid removal of C–N films from the wall surfaces of fusion devices.     

银杏叶中硼的形态分析

采用连续浸取方法分析银杏叶中硼的分布及形态.结果表明:银杏叶中各形态硼含量(质量分数,%)依次为:醋酸溶解态(34.36)>水溶态(12.82)>螯合态(9.60)>醇溶态(8.38)>残渣态(6.62)>盐溶态(5.66)>盐酸羟胺溶解态(3.21).测定结果对银杏中有效成分的利用有一定指导意义.     

The acylation and phosphorylation pattern of lipid A from Xanthomonas campestris strongly influence its ability to trigger the innate immune response in Arabidopsis

Lipopolysaccharides (LPSs) are major components of the cell surface of Gram-negative bacteria. LPSs comprise a hydrophilic heteropolysaccharide (formed by the core oligosaccharide and the O-specific polysaccharide) that is covalently linked to the glycolipid moiety lipid A, which anchors these macromolecules to the external membrane. LPSs are one of a group of molecules called pathogen-associated molecular patterns (PAMPs) that are indispensable for bacterial growth and viability, and act to trigger innate defense responses in eukaryotes. We have previously shown that LPS from the plant pathogen Xanthomonas campestris pv. campestris (Xcc) can elicit defense responses in the model plant Arabidopsis thaliana. Here we have extended these studies by analysis of the structure and biological activity of LPS from a nonpathogenic Xcc mutant, strain 8530. We show that this Xcc strain is defective in core completion and introduces significant modification in the lipid A region, which involves the degree of acylation and nonstoichiometric substitution of the phosphate groups with phosphoethanolamine. Lipid A that was isolated from Xcc strain 8530 did not have the ability to induce the defense-related gene PR1 in Arabidopsis, or to prevent the hypersensitive response (HR) that is caused by avirulent bacteria as the lipid A from the wild-type could. This suggests that Xcc has the capacity to modify the structure of the lipid A to reduce its activity as a PAMP. We speculate that such effects might occur in wild-type bacteria that are exposed to stresses such as those that might be encountered during plant colonization and disease.