Stability and Electronic Properties of Hydrogenated Zigzag Carbon Nanotube Focused on Stone-Wales Defect

We present a first-principles study of the chemisorption of hydrogen on a Stone-Wales （SW） defective carbon nanotube （10,0）. The investigated configurations include four configurations covering single defects and double defects. One hydrogen dimer adsorption is energetically favored on bonds shared by carbon heptagon-heptagon for configurations with the defect parallel to the tube axis compared with the carbon pentagon-hexagon sites for ones with a slanted defect. This different behavior is also demonstrated for hydrogen dimer chain adsorption, the favored site for the former ones is through the defect, which is the nearest neighbor site to defect for the latter ones. It is found that the energy band gaps of hydrogenated configurations may be enlarged or decreased by altering the adsorption site or defect position. The semiconductor-to-metal transition may occur for configurations with the defect or defects parallel to the tube axis due to low electronic localization. Our results highlight the interest of the interaction of multi-factor system by providing a detailed bond and position picture of a hydrogenated defective carbon nanotube （10,0）.

Lattice Boltzmann simulation study of anode degradation in solid oxide fuel cells during the initial aging process

For present solid oxide fuel cells(SOFCs),rapid performance degradation is observed in the initial aging process,and the dis-cussion of the degradation mechanism necessitates quantitative analysis.Herein,focused ion beam-scanning electron microscopy was em-ployed to characterize and reconstruct the ceramic microstructures of SOFC anodes.The lattice Boltzmann method(LBM)simulation of multiphysical and electrochemical processes in the reconstructed models was performed.Two samples collected from industrial-size cells were characterized,including a reduced reference cell and a cell with an initial aging process.Statistical parameters of the reconstructed microstructures revealed a significant decrease in the active triple-phase boundary and Ni connectivity in the aged cell compared with the reference cell.The LBM simulation revealed that activity degradation is dominant compared with microstructural degradation during the initial aging process,and the electrochemical reactions spread to the support layer in the aged cell.The microstructural and activity de-gradations are attributed to Ni migration and coarsening.

Characterization of 3D pore nanostructure and stress-dependent permeability of organic-rich shales in northern Guizhou Depression,China

The three-dimensional(3D)pore structures and permeability of shale are critical for forecasting gas production capacity and guiding pressure differential control in practical reservoir extraction.However,few investigations have analyzed the effects of microscopic organic matter(OM)morphology and 3D pore nanostructures on the stress sensitivity,which are precisely the most unique and controlling factors of reservoir quality in shales.In this study,ultra-high nanoscale-resolution imaging experiments,i.e.focused ion beam-scanning electron microscopy(FIB-SEMs),were conducted on two organic-rich shale samples from Longmaxi and Wufeng Formations in northern Guizhou Depression,China.Pore morphology,porosity of 3D pore nanostructures,pore size distribution,and connectivity of the six selected regions of interest(including clump-shaped OMs,interstitial OMs,framboidal pyrite,and microfractures)were qualitatively and quantitatively characterized.Pulse decay permeability(PDP)measurement was used to investigate the variation patterns of stress-dependent permeability and stress sensitivity of shales under different confining pressures and pore pressures,and the results were then used to calculate the Biot coefficients for the two shale formations.The results showed that the samples have high OM porosity and 85%of the OM pores have the radius of less than 40 nm.The OM morphology and pore structure characteristics of the Longmaxi and Wufeng Formations were distinctly different.In particular,the OM in the Wufeng Formation samples developed some OM pores with radius larger than500 nm,which significantly improved the connectivity.The macroscopic permeability strongly depends on the permeability of OM pores.The stress sensitivity of permeability of Wufeng Formation was significantly lower than that of Longmaxi Formation,due to the differences in OM morphology and pore structures.The Biot coefficients of 0.729 and 0.697 were obtained for the Longmaxi and Wufeng Formations,respectively.

Quantitative two/three-dimensional spatial characterization and fluid transport prediction of macro/micropores in Gaomiaozi bentonite

The sealing performance of a bentonite barrier is highly dependent on its seepage characteristics, which are directly related to the characteristics of its pore structure. Based on scanning electron microscopy(SEM) and focused ion beam-SEM(FIB-SEM), the pore structure of bentonite was characterized at different scales. First, a reasonable gray threshold was determined through back analysis, and the image was binarized based on the threshold. In addition, binary images were used to analyze bentonite’s pore structure(porosity and pore size distribution). Furthermore, the effects of different algorithms on the pore structure characterization were evaluated. Then, permeability calculations were performed based on the previous pore structure characteristics and a modified permeability prediction model. For permeability prediction based on the three-dimensional model, the effect of pore tortuosity was also considered. Finally, the accuracy of numerical calculations was verified by conducting macroscopic gas and alcohol permeability experiments. This approach provides a better understanding of the microscale mechanism of gas transport in bentonite and the importance of pore structures at different scales in determining its seepage characteristics.

Focused electron beam transport through a long narrow metal tube at elevated pressures in the forevacuum range

We present here our investigations of the features of focused electron beam transport in free space at elevated pressures of a few pascals.We have explored the effect of the beam accelerating voltage,operating gas pressure,and magnetic focusing upon the trajectory of beam electrons in the crossover region,in particular on the beam convergence and divergence angles.It is shown that for the forevacuum pressure range of 2-5 Pa explored,a distinctive feature of the propagation of a focused electron beam with a current of up to 20 mA at an accelerating voltage of 10-20 kV is the difference in the angles of convergence(before the focus)and divergence(after the focus).Whereas at a low pressure of 2 Pa the divergence angle is smaller than the convergence angle,as the pressure increases the divergence angle increases and for pressures greater than 5 Pa the divergence angle is greater than the convergence angle.The results obtained were used in experiments on electron beam transport through a long narrow metal tube with a diameter of 5.8-9.2 mm and length of 10-30 cm.We show that for a 30 cm long tube of 7.5 mm diameter,the focused beam transmission can exceed 70%.

Structural and mechanical properties of Al–C–N films deposited at room temperature by plasma focus device

The Al–C–N films are deposited on Si substrates by using a dense plasma focus（DPF） device with aluminum fitted central electrode（anode） and by operating the device with CH_4/N_2 gas admixture ratio of 1：1. XRD results verify the crystalline Al N（111） and Al_3CON（110） phase formation of the films deposited using multiple shots. The elemental compositions as well as chemical states of the deposited Al–C–N films are studied using XPS analysis, which affirm Al–N, C–C, and C–N bonding. The FESEM analysis reveals that the deposited films are composed of nanoparticles and nanoparticle agglomerates. The size of the agglomerates increases at a higher number of focus deposition shots for multiple shot depositions. Nanoindentation results reveal the variation in mechanical properties（nanohardness and elastic modulus）of Al–C–N films deposited with multiple shots. The highest values of nanohardness and elastic modulus are found to be about 11 and 185 GPa, respectively, for the film deposited with 30 focus deposition shots. The mechanical properties of the films deposited using multiple shots are related to the Al content and C–N bonding.

PERIODIC SOLUTIONS TO ELECTRON BEAMS FOCUSING SYSTEM

In this paper, we study a mathematical model of electron beam focusing system. We prove the existence of periodic solutions to the model using homotopy method.