Hexagonal CuSe nanoflakes with a lateral size of 200-800 nm and a thickness of 15-40 nm have been successfully synthesized by a concentrated alkaline hydrothermal method in which CuCl and Se powder were used as raw materials. Experimental results show that the amount of polyvinylpyrrolidone and the NaOH concentration play important roles in the formation of hexagonal CuSe nanoflakes. The photocatalytic activity of the as-synthesized hexagonal CuSe nanoflakes was investigated by the photocatalytic degradation of organic methylene blue (MB) under natural sunlight irradiation. It is found that hexagonal CuSe nanoflakes exhibit excellent photocatalytic activity and repeatability and above 99% MB in wastewater can be degraded after sunlight irradiation for 25 min in the presence of hydrogen peroxide.
In modern systems-on-chip (SOC) technology analog modules are costly to design. This paper studies an optimal realization of switched-capacitor (SC) circuit given a transfer function (TF) in the z-domain. Among the multiple possibilities of capacitance assignments, the proposed method is more controllable in arriving at a desirable SC realization. The underlying technique applies a symbolic method to derive a cancellation-free symbolic representation for a given SC circuit topology, then uses the automatically generated symbolic coefficient expressions to synthesize a set of numerical capacitance values suitable for physical implementation. Examples demonstrate the effectiveness of the proposal.
The switched-capacitor (SC) circuit realization problem is traditionally solved by heuristic algorithms. However, an algorithm-like simulated annealing (SA) is stochastic, and its behavior in solving a non-convex optimization problem is unpredictable. In this paper, we make an investigation on using a deterministic and a stochastic optimization algorithm for solving the realization problem of the classical Fleischer-Laker SC filter. By considering minimum area as the design goal, we prove that the a linear programming-based deterministic algorithm is capable of finding a global minimum. With the global optimality established, we then use an SA algorithm to solve the same problem in purpose of investigating the search capability of the SA algorithm. We find that the stochastic SA algorithm cannot always reach a suboptimal solution with quality comparable with the linear programming result. Other issues like convergence speed and the percentage of arriving at the global minimum are examined as well. This research exposes that understanding the underlying optimization problem structure for the realization of SC circuits is of fundamental meaning for developing more efficient heuristic algorithms.
An optimized scheme of pulse symmetrical position-orthogonal space-time block codes (PSP-OSTBC) is proposed and applied with m-pulse positions modulation (m-PPM) without the use of a complex decoding algorithm in an optical multi-input multi-output (MIMO) ultraviolet (UV) communication system. The proposed scheme breaks through the limitation of the traditional Alamouti code and is suitable for high-order m-PPM in a UV scattering channel, verified by both simulation experiments and field tests with specific parameters. The performances of 1×1, 2×1, and 2×2 PSP-OSTBC systems with 4-PPM are compared experimentally as the optimal tradeoff between modification and coding in practical application. Meanwhile, the feasibility of the proposed scheme for 8-PPM is examined by a simulation experiment as well. The results suggest that the proposed scheme makes the system insensitive to the influence of path loss with a larger channel capacity, and a higher diversity gain and coding gain with a simple decoding algorithm will be achieved by employing the orthogonality of m-PPM in an optical-MIMO-based ultraviolet scattering channel.
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