Optimal control problem in a domain with branched structure and homogenization

We consider a linear parabolic problem in a thick junction domain which is the union of a fixed domain and a collection of periodic branched trees of height of order 1 and small width connected on a part of the boundary. We consider a three‐branched structure, but the analysis can be extended to n‐branched structures. We use unfolding operator to study the asymptotic behavior of the solution of the problem. In the limit problem, we get a multi‐sheeted function in which each sheet is the limit of restriction of the solution to various branches of the domain. Homogenization of an optimal control problem posed on the above setting is also investigated. One of the novelty of the paper is the characterization of the optimal control via the appropriately defined unfolding operators. Finally, we obtain the limit of the optimal control problem. Copyright © 2016 John Wiley & Sons, Ltd.     

A schistosomiasis compartment model with incubation and its optimal control

A new mathematical model included an exposed compartment is established in consideration of incubation period of schistosoma in human body. The basic reproduction number is calculated to illustrate the threshold of disease outbreak. The existence of the disease free equilibrium and the endemic equilibrium are proved. Studies about stability behaviors of the model are exploited. Moreover, control measure assessments are investigated in order to seek out effective control interventions for anti‐schistosomiasis. Then, the corresponding optimal control problem according to the model is presented and solved. Theoretical analyses and numerical simulations induce several prevention and control strategies for anti‐schistosomiasis. At last, a discussion is provided about our results and further work. Copyright © 2017 John Wiley & Sons, Ltd.     

Composite Polybenzimidazole Membrane with High Capacity Retention for Vanadium Redox Flow Batteries

Currently, energy storage technologies are becoming essential in the transition of replacing fossil fuels with more renewable electricity production means. Among storage technologies, redox flow batteries (RFBs) can represent a valid option due to their unique characteristic of decoupling energy storage from power output. To push RFBs further into the market, it is essential to include low-cost materials such as new generation membranes with low ohmic resistance, high transport selectivity, and long durability. This work proposes a composite membrane for vanadium RFBs and a method of preparation. The membrane was prepared starting from two polymers, meta-polybenzimidazole (6 μm) and porous polypropylene (30 μm), through a gluing approach by hot-pressing. In a vanadium RFB, the composite membrane exhibited a high energy efficiency (~84%) and discharge capacity (~90%) with a 99% capacity retention over 90 cycles at 120 mA·cm⁻², exceeding commercial Nafion^® NR212 (~82% efficiency, capacity drop from 90% to 40%) and Fumasep^® FAP-450 (~76% efficiency, capacity drop from 80 to 65%).     

Synthesis,characterizations, and electrochemical studies of ZnO/reduced graphene oxide nanohybrids for supercapacitor application

Herein the present article reports the fabrication of ZnO/reduced graphene oxide (ZnG) nanohybrid following a reduction-based process using a non-hazardous material, i.e., ascorbic acid. The morphology, structure, and bonding in the nanohybrid were analyzed using different techniques. Atomic force microscopy and scanning electron microscopy images show spherical particles of ZnO distributed over reduced graphene oxide (rGO). The X-ray diffraction analysis gives calculated values of crystallite size for ZnO as 15.62 nm. The successful incorporation of ZnO nanoparticles into rGO was confirmed using energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. The electrochemical studies were performed using an electrolyte (0.5 M H₂SO₄). The calculated value of specific capacitance for the nanohybrid was 345 Fg^-1, which was found to be almost double as compared to that of rGO, which is having a value of only 190.5 Fg^-1 at the same scan rate. The nanohybrid also showed excellent capacitance retention after 1,000 cycles.     

Risk-averse stochastic optimal control: An efficiently computable statistical upper bound

In this paper, we discuss an application of the Stochastic Dual Dynamic Programming (SDDP) type algorithm to nested risk-averse formulations of Stochastic Optimal Control (SOC) problems. We propose a construction of a statistical upper bound for the optimal value of risk-averse SOC problems. This outlines an approach to a solution of a long standing problem in that area of research. The bound holds for a large class of convex and monotone conditional risk mappings. Finally, we show the validity of the statistical upper bound to solve a real-life stochastic hydro-thermal planning problem.     

半线性抛物最优控制问题全离散插值系数有限元方法的收敛性分析

本文考虑全离散插值系数有限元方法求解半线性抛物最优控制问题,其中控制变量用分片常数函数逼近,状态变量和对偶状态变量用分片线性函数逼近.对于方程中的半线性项,先用插值系数技巧处理,再用牛顿迭代法求解.通过引入一些辅助变量和投影算子,并利用有限元空间的逼近性质,得到半线性抛物最优控制问题插值系数有限元方法的收敛性结果;数值算例结果验证了理论结果的正确性.     

Li2MnO3 content effects on thermal,structural, electrical and electrochemical properties of xLi2MnO3-(1-x)LiNi0.9Zn0.1O2 cathode materials

xLi₂MnO₃-(1-x)LiNi_0.9Zn_0.1O₂ (x = 0.1, 0.2 and 0.3) cathodes were prepared by two steps solid-state reaction method. Layered crystalline phases (space groups of C2/m for Li₂MnO₃ and R3m for LiNi_0.9Zn_0.1O₂) were detected in all cathodes. FTIR study also revealed the formation of the layered-type structures of all cathodes. The structural parameters were greatly influenced by the contents of Li₂MnO₃ in xLi₂MnO₃-(1-x)LiNi_0.9Zn_0.1O₂. The electrical conductivities were found in the range of 1.2 × 10^?6 to 2.7 × 10^?6 S/cm. The dielectric spectra revealed the interfacial polarization Maxwell–Wagner type dielectric dispersion existing in all samples. The cathodes delivered the discharge capacities of 149 (x = 0.1), 151 (x = 0.2) and 157 mAh/g (x = 0.3) with capacity retention between 94.6 and 96.8% when they were cycled from 3.0 to 4.5 V under 0.1C rate. The x = 0.3 cathode exhibited the highest cyclic performance (96.8%) after 10 cycles due to its lower cations disorder.     

Fixed Final Time Optimal Control via Simple Cell Mapping

A cell mapping strategy based on Bellman'sPrinciple of optimality (BP) is proposed to solve the fixed final time optimalcontrol of strongly nonlinear systems with state and control bounds. Thefixed final time problem is transformed into a fixed final time-fixed finalstate optimal control problem by reversing the time. This transformationallows to solve the problem in the framework of the BP. Backward searchingalgorithms within the cell mapping context are used to obtain the solution ofthe new problem. This approach reduces considerably the computational effortrequired for the original problem when it is solved by a forward searchingapproach. The vibration control problem of damped and undamped variablestiffness oscillators with bounded stiffness tuning range is studied todemonstrate the effectiveness of the approach. A numerical study on theconvergence of the method is also presented.     

REMEDIATION OF POLLUTED SOILS BY UTILIZING HYDROTHERMALLY TREATED CALCAREOUS FLY ASHES

This paper investigates a treated fly ash to act as a synthetic zeolite to remediate soils polluted with heavy metals and metalloids （As, Pb, Cu, Zn, Fe, Cd and Mn）. Four types of such ＇zeolites＇ were synthesized by hydrothermal treatment of a calcareous fly ash derived from Greek lignite-fired power plants： two with excess of sodium hydroxide in a solid/liquid ratio of 50 g·L^-1, and two with excess of fly ash in a solid/liquid ratio of 100g·L^-1. Soil samples were obtained from a former mining site at Lavrion, Greece. Mobilization and transfer of metals to the retention agents was effected by using HCI aq 1M, with satisfactory results with respect to As, Pb, Cu, Mn and Cd. The great variety of metal complexes in soil was found to be of major importance for the effectiveness of the overall process. The final products were solidified either on their own, or by using additives such as lime and cement.     

一种最优控制的胞映射算法

由Hsu提出的利用胞映射进行最优控制的方法可以发展成实用的工程控制技术.本文以研究算法为出发点,利用胞映射的特性,结合实际的计算与可能,作了一系列旨在提高计算速度和节省内存的改进;并给出了简单有效的区分同耗最优控制对的统一的方法.使用平常的微型计算机也能有效地解决实际工程问题的最优控制.