温度对南方红豆杉种子萌发的影响

南方红豆杉作为一种重要的天然抗癌药物资源及园林树种,具有极大的经济价值,本文主啼杉种子休眠时间长,自然繁殖率低的问题,采用先在２０℃或２５℃层积处子５个月,然后再在５℃层积种子５个月,即有种子萌发,提早出苗率为３０％在右,综合出苗率达９２％,而自然温度层积种子则需１个月出苗,出苗率为８０％,说明南方红豆杉种子经先高温后低温高温层积,能有效缩短育苗周期,提高种子萌发率和成苗率。     

IV模型中变点序贯检验方法

本文研究了IV模型中变点序贯检验问题.提出了基于加权残差部分和(weighted-CUSUM)的检验统计量.证明了其在原假设和备择假设下的极限性质.该检验方法在特征量与跃度非正交性条件下,当δ=1/2具有非平凡势,而当0≤δ<1/2时,则是相合的.     

Robust Optimal Portfolio Choice Under Markovian Regime-switching Model

We investigate an optimal portfolio selection problem in a continuous-time Markov-modulated financial market when an economic agent faces model uncertainty and seeks a robust optimal portfolio strategy. The key market parameters are assumed to be modulated by a continuous-time, finite-state Markov chain whose states are interpreted as different states of an economy. The goal of the agent is to maximize the minimal expected utility of terminal wealth over a family of probability measures in a finite time horizon. The problem is then formulated as a Markovian regime-switching version of a two-player, zero-sum stochastic differential game between the agent and the market. We solve the problem by the Hamilton-Jacobi-Bellman approach.      

Exponential Decay of Lifetimes and a Theorem of Kac on Total Occupation Times

Let be the Dirichlet integral and the Brownian motion on R. Let be a finite positive measure in the Kato class and the additive functional associated with . We prove that for a regular domain D of R ^d

一种基于统计分析的图像变化检测方法

为了更准确地从两幅同一地区不同时间的遥感图像中检测出地物的变化情况,提出一种基于统计分析的方法.即：统计检验方法.这种方法是将局部回归方法应用于两幅不同时间遥感图像中的同一感兴趣矩形区域,当回归系数表现出较大的差异时,这些图像区域被分割成更小的子区域.与传统的变化检测方法相比,统计检验法不仅与脉冲噪音无关,而且也不受传感器灵敏度降低引起的外部变化和光源位置变化的影响.     

Europium-decorated graphene quantum dots as a fluorescent probe for label-free,rapid and sensitive detection of Cu and l-cysteine

In this work, europium-decorated graphene quantum dots (Eu-GQDs) were prepared by treating three-dimensional Eu-decorated graphene (3D Eu-graphene) via a strong acid treatment. Various characterizations revealed that Eu atoms were successfully complexed with the oxygen functional groups on the surface of graphene quantum dots (GQDs) with the atomic ratio of 2.54%. Compared with Eu free GQDs, the introduction of Eu atoms enhanced the electron density and improved the surface chemical activities of Eu-GQDs. Therefore, the obtained Eu-GQDs were used as a novel “off-on” fluorescent probe for the label-free determination of Cu²⁺ and l-cysteine (L-Cys) with high sensitivity and selectivity. The fluorescence intensity of Eu-GQDs was quenched in the presence of Cu²⁺ owing to the coordination reaction between Cu²⁺ and carboxyl groups on the surface of the Eu-GQDs. The fluorescence intensity of Eu-GQDs recovered with the subsequent addition of L-Cys because of the strong affinity of Cu²⁺ to L-Cys via the Cu–S bond. The experimental results showed that the fluorescence variation of the proposed approach had a good linear relationship in the range of 0.1–10 μM for Cu²⁺ and 0.5–50 μM for L-Cys with corresponding detection limits of 0.056 μM for Cu²⁺ and 0.31 μM for L-Cys. The current approach also displayed a special response to Cu²⁺ and L-Cys over the other co-existing metal ions and amino acids, and the results obtained from buffer-diluted serum samples suggested its applicability in biological samples.     

An XPS Study of Perovskite Oxides RECr03

Perovskite Oxides RECr0₃ (RE=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb) were prepared by the means of solid state reaction.The measurments of XRD and XPS showed that the replacement by rare earth element lowers the binding energy(BE) of rare earth ions, compared with their sesquioxides. In the Perovskite Oxides, the BE of Cr2p_3/2 increases with the decrease of ionic radius of the RE ion.The reason for the changes of BE are discussed.     

Optically Controlled Recovery and Recycling of Homogeneous Organocatalysts Enabled by Photoswitches

We address a critical challenge of recovering and recycling homogeneous organocatalysts by designing photoswitchable catalyst structures that display a reversible solubility change in response to light. Initially insoluble catalysts are UV-switched to a soluble isomeric state, which catalyzes the reaction, then back-isomerizes to the insoluble state upon completion of the reaction to be filtered and recycled. The molecular design principles that allow for the drastic solubility change over 10 times between the isomeric states, 87 % recovery by the light-induced precipitation, and multiple rounds of catalyst recycling are revealed. This proof of concept will open up opportunities to develop highly recyclable homogeneous catalysts that are important for the synthesis of critical compounds in various industries, which is anticipated to significantly reduce environmental impact and costs.