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This paper investigates the problem of secure energy efficiency maximization for a reconfigurable intelligent surface (RIS) assisted uplink wireless communication system, where an unmanned aerial vehicle (UAV) equipped with an RIS works as a mobile relay between the base station (BS) and a group of users. We focus on maximizing the secure energy efficiency of the system via jointly optimizing the UAV's trajectory, the RIS's phase shift, users' association and transmit power. To tackle this problem, we divide the original problem into three sub-problems, and propose an efficient iterative algorithm. In particular, the successive convex approximation method (SCA) is applied to solve the nonconvex UAV trajectory, the RIS's phase shift, and transmit power optimization sub-problems. We further provide two schemes to simplify the solution of phase and trajectory sub-problem. Simulation results demonstrate that the proposed algorithm converges fast, and the proposed design can enhance the secure energy efficiency by up to 38\% gains, as compared to the traditional schemes without any RIS.

We demonstrate the optical absorption has been enhanced in the small molecule organic solar cells by employing trapezoid grating structure. The enhanced absorption is mainly attributed to both waveguide modes and surface plasmon modes, which has been simulated by using finite-difference time-domain method. The simulated results show that the surface plasmon along the semitransparent metallic Ag anode is excited by introducing the periodical trapezoid gratings, which induce high intensity field increment in the donor layer. Meanwhile, the waveguide modes result a high intensity field in acceptor layer. The increment of field improves the absorption of organic solar cells, significantly, which has been demonstrated by simulating the electrical properties. The simulated results exhibiting 31 % increment of the short-circuit current has been achieved in the optimized device, which is supported by the experimental measurement. The power conversion efficiency of the grating sample obtained in experiment exhibits an enhancement of 7.7 %.

This paper provides an overview of the policies, process, and practice of special education in the People's Republic of China. Individual sections address the following topics: historical perspectives; legislative highlights (especially China's 1986 compulsory education law and the law on the protection of people with disabilities passed in 1991); the purpose of special education; the legal definition of disability; classification and prevalence of disabilities (concluding that 4.9 percent of the total population is disabled); service delivery options (special schools, special classes, and regular class placement); number of children receiving services (fewer than 200,000 out of about 8 million children with disabilities are receiving special education services); curricula perspectives (which adhere to a national model and stress group instruction); personnel preparation (only 5 of 1,075 universities train special educators); adult services (emphasis is on enhancing employment opportunities); and family education (some parent education efforts are underway). The tremendous growth of special education in China over the past 15 years is noted. Four tables provide incidence figures of children with disabilities and trends since 1980, and course requirements in teacher preparation programs. Contains nine references. (DB)