A first-principles study of MgB2 (0001) surfaces

We report self-consistent {\it ab initio} calculations of structural and electronic properties for the B- and Mg-terminated MgB$_{2}$ (0001) surfaces. We employ ultra-soft pseudopotentials and plane wave basis sets within the generalized gradient approximation. The surface relaxations are found to be small for both B- and Mg-terminated surfaces. For the B-terminated surface, both B ${\sigma}$ and ${\pi}$ surface bands appear, while only one B ${\pi}$ surface band exists near the Fermi level for the Mg-terminated surface. The superconductivity of the MgB$_2$ surfaces is discussed. The work function is predicted to be 5.95 and 4.25 eV for the B- and Mg-terminated surfaces respectively. The simulated scanning tunneling microscopy images of the surfaces are not sensitive to the sign and value of the bias voltages, but depend strongly on the tip-sample distance. An image reversal is predicted for the Mg-terminated surface.Comment: 3 pages, 4 figures, Revte

Mass fractionation processes of transition metal isotopes

Macromolecular Biochemistr

Quantifying atmospheric nitrogen deposition through a nationwide monitoring network across China

A Nationwide Nitrogen Deposition Monitoring Network (NNDMN) containing 43 monitoring sites was established in China to measure gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− in air and/or precipitation from 2010 to 2014. Wet/bulk deposition fluxes of Nr species were collected by precipitation gauge method and measured by continuous-flow analyzer; dry deposition fluxes were estimated using airborne concentration measurements and inferential models. Our observations reveal large spatial variations of atmospheric Nr concentrations and dry and wet/bulk Nr deposition. On a national basis, the annual average concentrations (1.3–47.0 μg N m−3) and dry plus wet/bulk deposition fluxes (2.9–83.3 kg N ha−1 yr−1) of inorganic Nr species are ranked by land use as urban > rural > background sites and by regions as north China > southeast China > southwest China > northeast China > northwest China > Tibetan Plateau, reflecting the impact of anthropogenic Nr emission. Average dry and wet/bulk N deposition fluxes were 20.6 ± 11.2 (mean ± standard deviation) and 19.3 ± 9.2 kg N ha−1 yr−1 across China, with reduced N deposition dominating both dry and wet/bulk deposition. Our results suggest atmospheric dry N deposition is equally important to wet/bulk N deposition at the national scale. Therefore, both deposition forms should be included when considering the impacts of N deposition on environment and ecosystem health

Simultaneously enhanced strength and ductility of Cu-xGe alloys through manipulating the stacking fault energy (SFE)

Vinogradov et al. [1] reported that the stacking fault energy (SFE) of Cu-xGe alloys with germanium concentration varying from 0, 0.1, 5.7 to 9.0 at% alters from 78, 54, 15 to 8 mJ/m2 , respectively. In the present study, the Cu-xGe alloys were prepared by forging at the liquid nitrogen temperature and their mechanical properties were systematically investigated. Results indicated that the microhardness, strength and uniform elongation of Cu-xGe alloys were simultaneously improved by lowering the SFE. X-ray diffraction measurements revealed that a reduction in SFE leads both to a decrease in grain size and an increase in dislocation density, twin density and microstrain for the cryogenic forged samples and these contribute to the improvements in the mechanical properties. This work demonstrates that high strength and excellent ductility can be simultaneously achieved by lowering SFE of the metals

CD4(+)CD25(+)Tregs express an increased LAG-3 and CTLA-4 in anterior chamber-associated immune deviation

Background Regulatory CD4+CD25+ T cells have been proven to be essential for maintenance of peripheral tolerance and autoimmune diseases. ACAID is a model of immune privilege in the eye. Relatively little is known about the role and phenotype of these regulatory CD4+CD25+ T cells in ACAID. Methods Injection of OVA into the anterior chamber of BALB/C mice was performed to induce ACAID. The frequencies of splenic CD4+CD25+ Tregs and the expression of CTLA-4 and LAG-3 on these cells were determined by flow cytometry. Magnetic cell sorting was used to isolate CD4+CD25+ and CD4+CD25¿T cells. The function of CD4+CD25+ T cells was detected by in vitro immunosuppression assays and in vivo adoptive transfer. Results ACAID was successfully induced following an i.c. injection of OVA. Frequencies of CD4+CD25+ and Tregs were significantly increased in ACAID mice as compared to those in controls. The CD4+CD25+ T cells stimulated with OVA in ACAID mice showed a stronger suppressive ability in vitro than those seen in non-ACAID mice. CD4+CD25+ T cells from ACAID mice, but not from non-ACAID mice, were able to suppress DTH responses in an antigen-specific manner following adoptive transfer. The frequencies of CTLA-4 or LAG-3 on Tregs in ACAID mice were higher as compared with those in naive mice. Conclusion Splenic CD4+CD25+Foxp3+T cells expressing CTLA4 and LAG3 play an important role in the induction of ACAI