Geometry Dependent Current-Voltage Characteristics of ZnO Nanostructures: A Combined Nonequilibrium Green’s Function and Density Functional Theory Study

Current-voltage I-V characteristics of different ZnO nanostructures were studied using a combined nonequilibrium Green’s function and density functional theory techniques with the two-probe model. It was found that I-V characteristics of ZnO nanostructures depend strongly on their geometry. For wurtzite ZnO nanowires, currents decrease with increasing lengths under the same applied voltage conditions. The I-V characteristics are similar for single-walled ZnO nanotubes and triangular cross section ZnO nanowires but they are different from I-V characteristics of hexagonal cross section ZnO nanowires. Finally, our results are discussed in the context of calculated transmission spectra and densities of states

Research progress on metallurgical processing of solar grade multicrystalline silicon

Compared with preparation of solar grade multicrystalline silicon(SOG-Si) by improved Siemens method,new silane method and fluidized bed method,metallurgical processing of SOG-Si is considered as an important way to solve the shortage of silicon feedstock supply and to reduce costs for Photovoltaic industry,which has promoted signification to the widespread use of solar energy.The fundamental principles of removal of metallic and non-metallic impurities in metallurgical grade silicon(MG-Si) during metallurgical processing of SOG-Si is discussed,and research progress on metallurgical processing technologies of SOG-Si is introduced

Preparation of Al/Si functionally graded materials using ultrasonic separation method

Functionally graded materials (FGM) have been widely used in many industries such as aerospace, energy and electronics. In this experimental study of fabricating FGM, an approach was developed to prepare Al/Si FGM using power ultrasonic separation method. Material sample with continuously changing composition and performance/properties was successfully produced. Results showed that the microstructure of the FGM sample transited, from its top to bottom, from the hypereutectic structure with a large quantity of primary Si gradually to the eutectic, and fi nally to the hypoeutectic with numerous primary Al dendrites. The distribution of primary Si and microhardness of the FGM sample also presented graded characteristics, resulting that the wear resistance of the FGM sample decreased from top to bottom. Preliminary discussion was made on the mechanism of the formation of Al/Si FGM

Agricultural Water Allocation under Uncertainty: Redistribution of Water Shortage Risk.

This article develops an economic model to analyze how the risk of water shortages affects farmers’ land irrigation decision and how the priority-based water sharing arrangement redistributes such a risk among farms with different water rights priorities. The analysis brings together an array of comprehensive data files on irrigation rights, water supplies, and agricultural land use from eastern Idaho. Results indicate that a more left-skewed distribution of streamflow significantly discourages land irrigation among farmers except the most senior rights holders. The priority-based water sharing arrangement redistributes the macroscale risk of water shortages and thus exposes farmers of different water rights priorities to heterogeneous levels of risk: senior water rights holders are affected the least and such a risk is instead passed mostly on to junior water rights holders. The role of water rights in risk redistribution is more significant when the probability distribution of water shortage risk is asymmetric rather than symmetric. The historical development pattern of water rights influences how the priority of water rights takes effect on land irrigation decision

Research on vacuum-electromagnetic casting of IN100 superalloy ingots

In order to improve the inner quality of superalloy master alloy ingots, the new technology of superalloy vacuum-electromagnetic casting, i.e. applying electromagnetic stirring (EMS) to the solidification process of superalloy vacuum casting was developed. The effect of EMS on the inner quality of IN100 superalloy ingots was studied with EPMA and optical microscope. The results show that while an EMS with 50 Hz frequency and 60 A current is imposed, the equiax crystals of IN100 superalloy ingots can be effectively refined and increased, and the central shrinkage porosity and the dendritic segregation of IN100 superalloy ingots are greatly reduced, so the inner quality of IN100 superalloy ingots is obviously improved

Degassing effect and grain refinement of Al-Si alloy under ultrasound field

Under different constant temperatures a Al-1%Si alloy (mass fraction) melt was treated by ultrasound field. The gas content in Al-Si melt decreased obviously when the treated time is 60 s. The grains are refined and globularization when the Al-Si melt was solidified under ultrasound but the grains only are refined when solidified at isothermal temperature in the mushy zone with ultrasonic vibrations. The results imply that the expansion and collapse of cavities which results in the formation of nuclei play the important role in the formation of fine and globular grains

A Criterion for Topological Close-Packed Phase Formation in High Entropy Alloys

The stability of topological close-packed (TCP) phases were found to be well related to the average value of the d-orbital energy level $\overline{Md}$ for most reported high entropy alloys (HEAs). Excluding some HEAs that contain high levels of the elements aluminum and vanadium, the results of this study indicated that the TCP phases form at $\overline{Md}$ > 1.09. This criterion, as a semi-empirical method, can play a key role in designing and preparing HEAs with high amounts of transitional elements