磺酰脲类除草剂分子印迹聚合物制备及应用研究进展

磺酰脲类除草剂本身易降解,在环境和生物样品中痕量存在,其残留分析工作颇具挑战。分子印迹聚合物因其良好的选择性和稳定性已被广泛应用于农药残留分析的分离与富集前处理过程,提高了检测的准确度和精密度。本文从单体、溶剂与致孔剂、聚合方法三个方面概述了近15年来磺酰脲类分子印迹聚合物的制备,并对其在残留检测中的应用方式进行了综述,为磺酰脲类除草剂残留检测技术的进一步开发提供了参考。     

正相液相色谱-串联质谱法分离普萘洛尔对映体

建立正相液相色谱-串联质谱(LC-MS/MS)分离普萘洛尔对映体的方法,并用于盐酸普萘洛尔片对映体含量测定.样品使用甲醇进行简单提取,采用Chiralcel OD-H手性柱,以正己烷-乙醇-氨水(70∶30∶0.4, v/v/v)为流动相,流速为0.4 mL/min.在正离子模式下,通过电喷雾离子化(ESI+),采用多...     

A new globalization technique for nonlinear conjugate gradient methods for nonconvex minimization

It is well-known that the HS method and the PRP method may not converge for nonconvex optimization even with exact line search. Some globalization techniques have been proposed, for instance, the PRP+ globalization technique and the Grippo-Lucidi globalization technique for the PRP method. In this paper, we propose a new efficient globalization technique for general nonlinear conjugate gradient methods for nonconvex minimization. This new technique utilizes the information of the previous search direction sufficiently. Under suitable conditions, we prove that the nonlinear conjugate gradient methods with this new technique are globally convergent for nonconvex minimization if the line search satisfies Wolfe conditions or Armijo condition. Extensive numerical experiments are reported to show the efficiency of the proposed technique.     

代数κ-拟-A类算子的Weyl定理

若T或T~*是无穷维可分的Hilbert空间H上的代数κ-拟-A类算子,则Weyl定理对任意的f∈H(σ(T))成立,其中H(σ(T))为σ(T)的开邻域上解析函数的全体.若T~*是代数κ-拟-A类算子,则a-Weyl定理对f(T)成立。还证明了若T或T~*是代数κ-拟-A类算子,则Weyl谱与本质近似点谱的谱映射定理对f(T)成立.     

A non‐autonomous epidemic model with time delay and vaccination

In this paper, a non‐autonomous SIRVS epidemic model with time delay and vaccination is investigated. We assume that the vaccinated have a constant immunity period. Some new threshold conditions are obtained. These threshold conditions govern the extinction and permanence of the disease. When the model degenerates into the periodic or autonomous case, the corresponding basic reproduction number can be derived from these threshold conditions. Copyright © 2009 John Wiley & Sons, Ltd.     

One‐step fabrication of SnxTi1‐xO2 rutile‐type core‐shell microspheres and their electrochemical properties

Sn_xTi_1‐xO₂ core‐shell microspheres were synthesized through a simple one‐step hydrothermal method. The structural and morphologic properties were unambiguously characterized, and the electrochemical performance of the Sn_xTi_1‐xO₂ microspheres was determined by cyclic voltammetry. The possible formation mechanism of Sn_xTi_1‐xO₂ microspheres was also proposed.     

Dye-sensitized phototransformation of chlorophenols and their subsequent chemiluminescence reactions

A novel chemiluminescence (CL) reaction of chlorophenols (CPs), including 2-chlorophenol (2-CP), 4-CP, 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) was reported, which was based on the oxidation of the phototransformed CPs by N-bromosuccinimide (NBS). It was found that the dye-sensitized phototransformation is a prerequisite for the subsequent CL reaction, and the presence of 1.9×10^-2 mol L⁻¹ Triton X-100 or 3.7×10^-3 mol L⁻¹ CTAB can greatly enhance the CL intensity. A neutral sample solution with the presence of 2×10^-5 mol L⁻¹ fluorescein (FL) was found to be optimum for the phototransformation of 2-CP, 4-CP, 2,4-DCP and PCP, but a lower pH of 5.3 was more suitable for 2,4,6-TCP. Based on the CL reaction, detection limits of 8.6×10⁻⁸, 1.1×10⁻⁷, 1.5×10^-7, 4.6×10^-8 and 3.0×10⁻⁵ mol L⁻¹ were achieved, respectively, for 2-CP, 4-CP, 2,4-DCP, 2,4,6-TCP and PCP with the optimized conditions in the flow system. The mechanism of the phototransformation and the subsequent CL reaction were preliminarily studied and it was suggested that the singlet oxygen formed in the dye-sensitization process was responsible for the conversion of CPs into light-emitting precursors. These intermediate products were suggested to be peroxide compounds after testing by a luminal-based post-column CL detection experiment.     

The extremal irregularity of connected graphs with given number of pendant vertices

Czechoslovak Mathematical Journal - The irregularity of a graph G = (V, E) is defined as the sum of imbalances ∣du ? dv∣ over all edges uv ∈ E, where du denotes the degree...     

Control of a multigroup COVID-19 model with immunity: treatment and test elimination

Nonlinear Dynamics - This paper introduces a multigroup COVID-19 model with immunity, in which the total population of each group is partitioned into five compartments, that is, susceptible,...