Graphene nanoplatelet (GNP)-reinforced aluminum oxide (Al 2 O 3 ) composites were sintered by spark plasma sintering in three different compositions (0, 0·5, 5 vol.% GNPs). To investigate the effects of graphene addition on the composites' wear resistance, ball-on-disk wear tests were conducted under very high normal load (40 N) by using a 3-mm-dia. ceramic counterface. Aluminum oxide-0·5 vol.% GNP exhibited 65% improvement in the wear resistance, while aluminum oxide-5 vol.% GNP displayed 53% poorer wear resistance as compared with aluminum oxide. The coefficient of friction was 0·45 for aluminum oxide-0·5 vol.% GNP, 0·40 for aluminum oxide-5 vol.% GNP and 0·60 for aluminum oxide. The highest wear resistance of aluminum oxide-0·5 vol.% GNP is attributed to formation of a continuous, protective and ultrathin graphene tribofilm on the wear surface. Tribofilm formation occurs due to the high shear forces induced by countersurface movement and localized heating, which causes GNP's delamination, overlap and welding together. In the case of aluminum oxide-5 vol.% GNP, poor dispersion and agglomeration of GNP results in a thick and discontinuous graphene tribofilm, which does not protect from the brittle fracture of aluminum oxide grains during wear.

Software product line (SPL) engineering manages families of software products that share common features. However, cost-effective test case generation for an SPL is challenging. Applying existing test case generation techniques to each product variant separately may test common code in a redundant way. Moreover, it is difficult to share the test results among multiple product variants. In this paper, we propose the use of centralization, which combines multiple product variants from the same SPL and generates test cases for the entire system. By taking into account all variants, our technique generally avoids generating redundant test cases for common software components. Our case study on three SPLs shows that compared with testing each variant independently, our technique is more efficient and achieves higher test coverage.

Solar photovoltaic driven air conditioning (PVAC) system with electricity storage is proposed as a good solution to help shifting peak load and consuming solar energy. In this paper, a grid-connected PVAC system using the TRNSYS simulation model consisting of PV panels, traditional air conditioners (TAC), power conditioning units, inverters, and grid connection equipment is proposed to investigate the economic feasibility compared with the traditional air conditioner. In the PVAC system, the electricity, firstly generated by PV panels and then stored in battery, is consumed by a DC inverter air conditioner to maintain the temperature of the room and the surplus electricity is sold to the grid. A life cycle cost comparison between PVAC system, traditional air conditioning system, and decomposed PV and air conditioning systems of three typical application cases is conducted, in which the operation conditions are based on the present circumstances of China. The results show that, in comparison with conventional air conditioners, better economic benefits can be achieved when the peak load of the air conditioning system is over a certain value. Sensitivity analysis is conducted to evaluate the effects caused by variation of economic assumptions. At last, a new operation model is proposed to achieve more benefits for the system.