Beihang University

About: Beihang University is a education organization based out in Beijing, China. It is known for research contribution in the topics: Control theory & Microstructure. The organization has 67002 authors who have published 73507 publications receiving 975691 citations. The organization is also known as: Beijing University of Aeronautics and Astronautics.

Orientation and size dependence of the elastic properties of zinc oxide nanobelts

Abstract: Molecular dynamics simulations are performed to characterize the response of zinc oxide (ZnO) nanobelts to tensile loading. The ultimate tensile strength (UTS) and Young's modulus are obtained as functions of size and growth orientation. Nanobelts in three growth orientations are generated by assembling the unit wurtzite cell along the [0001], , and crystalline axes. Following the geometric construction, dynamic relaxation is carried out to yield free-standing nanobelts at 300 K. Two distinct configurations are observed in the [0001] and orientations. When the lateral dimensions are above 10 A, nanobelts with rectangular cross-sections are seen. Below this critical size, tubular structures involving two concentric shells similar to double-walled carbon nanotubes are obtained. Quasi-static deformations of belts with and orientations consist of three stages, including initial elastic stretching, wurtzite-ZnO to graphitic-ZnO structural transformation, and cleavage fracture. On the other hand, [0001] belts do not undergo any structural transformation and fail through cleavage along (0001) planes. Calculations show that the UTS and Young's modulus of the belts are size dependent and are higher than the corresponding values for bulk ZnO. Specifically, as the lateral dimensions increase from 10 to 40 A, decreases between 38–76% and 24–63% are observed for the UTS and Young's modulus, respectively. This effect is attributed to the size-dependent compressive stress induced by tensile surface stress in the nanobelts. and nanobelts with multi-walled tubular structures are seen to have higher values of elastic moduli (~340 GPa) and UTS (~36 GPa) compared to their wurtzite counterparts, echoing a similar trend in multi-walled carbon nanotubes.

Corrosion‐Resistant Superhydrophobic Coatings on Mg Alloy Surfaces Inspired by Lotus Seedpod

Abstract: Superhydrophobic surfaces are widely found in nature, inspiring the development of excellent antiwater surfaces with barrier coatings isolating the underlying materials from the external environment. Here, the naturally occurring superhydrophobicity of lotus seedpod surfaces is reported. Protective coatings that mimic the lotus seedpod are fabricated on AZ91D Mg alloy surfaces with the synergistic effect of robust superhydrophobicity and durable corrosion resistance. The predesigned titanium dioxide films are coated on AZ91D by an in situ hydrothermal synthesis technique. Through sonication assisted electroless plating combined with a self-assembling method, the densely packed Cu-thiolate layers are uniformly plated with robust adhesion on the Mg alloy substrate, which function as a superhydrophobic barrier that can hold back the transport of water and corrosive ions contained such as Cl−. Notably, the two extreme wetting behaviors (superhydrophilicity and superhydrophobicity) as well as corrosion resistance and improved corrosion resistance can be easily controlled by removal of the hydrophobic materials (n-dodecanethiol) at elevated temperature (350 °C) and modifying them at room temperature for 18 cycles, indicative of exceptional adhesion between the superhydrophobic coating and the underlying AZ91D Mg alloy.

Substantial emission reductions from Chinese power plants after the introduction of ultra-low emissions standards

Abstract: In 2014, China introduced an ultra-low emissions (ULE) standards policy for renovating coal-fired power-generating units to limit SO2, NOx and particulate matter (PM) emissions to 35, 50 and 10 mg m−3, respectively. The ULE standard policy had ambitious levels (surpassing those of all other countries) and implementation timeline. We estimate emission reductions associated with the ULE policy by constructing a nationwide, unit-level, hourly-frequency emissions dataset using data from a continuous emissions monitoring systems network covering 96–98% of Chinese thermal power capacity during 2014–2017. We find that between 2014 and 2017 China’s annual power emissions of SO2, NOx and PM dropped by 65%, 60% and 72%, respectively. Our estimated emissions using actual monitoring data are 18–92% below other recent estimates. We detail the technologies used to meet the ULE standards and the determinants of compliance, underscoring the importance of ex post evaluation and providing insights for other countries wishing to reduce their power emissions. In 2014 China proposed an ultra-low emissions policy for coal-fired power plants to reduce emissions. Using comprehensive nationwide stack emissions monitoring data, Tang et al. show reductions in excess of 60% for SO2, NOx and particulate matter emissions since 2014, even as power generation overall increased.