Multi-period mean–variance portfolio selection with regime switching and a stochastic cash flow

This paper investigates a non-self-financing portfolio optimization problem under the framework of multi-period mean–variance with Markov regime switching and a stochastic cash flow. The stochastic cash flow can be explained as capital additions or withdrawals during the investment process. Specially, the cash flow is the surplus process or the risk process of an insurer at each period. The returns of assets and amount of the cash flow all depend on the states of a stochastic market which are assumed to follow a discrete-time Markov chain. We analyze the existence of optimal solutions, and derive the optimal strategy and the efficient frontier in closed-form. Several special cases are discussed and numerical examples are given to demonstrate the effect of cash flow.     

连续灰度铁电液晶器件制备

采用N*-Sc*序列相铁电液晶,通过控制在N*-Sc*相变时施加电压的频率和幅值,制备了不同分子层排列结构的器件,获得了“V”字形和半“V”字形的电光特性曲线,从而可以实现连续灰度.根据铁电液晶自发偶极矩与电场力矩的相互作用原理,分析了器件形成不同分子层排列结构及呈现“V”字形和半“V”字形电光特性的原因.     

高纯度2,6-二羟基萘的制备工艺

以便宜的2,6-萘二磺酸钠为原料,通过一步混合碱高温碱熔法合成高纯度2,6-二羟基萘。 N₂气保护下,添加苯酚或抗氧剂1010防止过度氧化焦油的产生,能显著提高2,6-二羟基萘收率。 较佳反应条件为:2,6-萘二磺酸钠与混合碱的质量比1:3,混合碱中氢氧化钠和氢氧化钾质量比2:1,使用0.5 g苯酚或抗氧剂1010,反应温度345 ℃,反应时间2 h,碱熔收率达到86.3%。 经过甲醇-水混合溶剂精制,2,6-二羟基萘纯度能达到99%。     

Enhanced Recyclability,Stability, and Selectivity of CdS/C@Fe3O4 Nanoreactors for Orientation Photodegradation of Ciprofloxacin

A unique CdS/C@Fe₃O₄ nanoreactor was fabricated by the surface‐imprinting technique, which effectively enhances the recyclability, stability, and selectivity for orientation recognition and photodegradation of ciprofloxacin in the binary mixed solution under visible‐light irradiation. This work not only puts forward a novel design idea that develops the potential application value of CdS, but also provides a new approach for inhibiting its secondary pollution.     

The structure and luminescence properties of long afterglow phosphor Y3−xMnxAl5−xSixO12

A series of phosphors with the composition Y_3−xMn_xAl_5−xSi_xO₁₂ (x=0, 0.025, 0.050, 0.075, 0.150, 0.225, 0.300) were prepared with solid state reactions. The X-ray powder diffraction analysis of samples shows that the substitution of Mn²⁺ and Si⁴⁺ does not change the garnet structure of phosphors, but makes the interplanar distance decrease to a certain extent. The emission spectra show that Mn²⁺ in Y₃Al₅O₁₂ emits yellow-orange light in a broad band. With the increment of substitution content, the emission intensity of the phosphors increases firstly then decreases subsequently, and the emission peak moves to longer wavelength. Afterglow spectra and decay curves show that all the Mn²⁺ and Si⁴⁺ co-doped samples emit yellow-orange light with long afterglow after the irradiation of ultraviolet light. The longest afterglow time is 18 min. Thermoluminescence measurement shows that there exist two kinds of traps with different depth of energy level and their depth decreases with the increment of substitution content.     

Investigation on Eu doped Sr2MgSi2O7 red-emitting phosphors for white-light-emitting diodes

In this work, we report the high temperature solid-state synthesis of red phosphors Sr₂MgSi₂O₇: Eu³⁺ with various Eu³⁺ concentrations. Their luminescent properties at room temperature are investigated. The X-ray diffraction patterns indicate that the red phosphors powder conforms to the tetragonal Sr₂MgSi₂O₇. Impurity structure appears when more than 20% Eu³⁺ is doped. The samples show a strong emission line at 615 nm and the intensity increases with the increase of Eu³⁺ concentration until concentration quenching occurs. Charge compensation assists in the reduction of the impurity structure and vacancies; hence the luminescent intensity is enhanced. The decay measurement indicates that the lifetime of Eu³⁺ emission is about 2-3 ms. Some of the Eu³⁺ can be reduced to Eu²⁺; this is also discussed.     

基于动态VaR约束与随机波动率模型的最优投资策略

研究Stein-Stein随机波动率模型下带动态VaR约束的最优投资组合选择问题. 假设投资者的目标是最大化终端财富的期望幂效用,可投资于无风险资产和一种风险资产, 风险资产的价格过程由Stein-Stein随机波动率模型刻画. 同时, 投资者期望能在投资过程中利用动态VaR约束控制所面对的风险.运用Bellman动态规划方法和Lagrange乘子法, 得到了该约束问题最优策略的解析式及特殊情形下最优值函数的解析式; 并通过理论分析和数值算例, 阐述了动态VaR约束与随机波动率对最优投资策略的影响.     

CVaR鲁棒均值-CVaR投资组合模型与求解

传统的均值-风险(包括方差、VaR、CVaR等)组合选择模型在计算最优投资组合时,常假定均值是已知的常值,但在实际资产配置中,收益的均值估计会有偏差,即存在着估计风险.在利用CVaR测度估计风险的基础上,研究了CVaR鲁棒均值-CVaR投资组合选择模型,给出了另外两种不同的求解方法,即对偶法和光滑优化方法,并探讨了它们的相关性质及特征,数值实验表明在求解大样本或者大规模投资组合选择问题上,对偶法和光滑优化方法在计算上是可行且有效的.     

Luminescence and red long afterglow investigation of Eu3+–Sm3+ CO-doped CaWO4 phosphor

A series of Eu³⁺–Sm³⁺ co-doped CaWO₄ phosphors were synthesized by the high temperature solid-state method. The crystal structure of the obtained samples was identified by XRD, and the results showed that all the phases were indexed to scheelite structure. The effect of the doping concentration of Sm³⁺ on the luminescent properties of the obtained products was investigated, and the optimal Sm³⁺ concentration was experimentally determined to 0.5%. The photoluminescence properties indicate that there is an efficient energy transfers from Sm³⁺ to Eu³⁺. The energy-transfer process between Sm³⁺ and Eu³⁺ was also given. Red long afterglow originating from the ⁵D₀–⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ was observed after samples were excited by 254 nm, and the duration of the optimal sample can last more than 35 min in dark with naked eyes. The proposed explanation for the afterglow property was also discussed.