Dynamical behavior for an eco-epidemiological model with discrete and distributed delay

In this paper, the dynamical behavior of an eco-epidemiological model with discrete and distributed delay is studied. Sufficient conditions for the local asymptotical stability of the nonnegative equilibria are obtained. We prove that there exists a threshold value of the feedback time delay τ beyond which the positive equilibrium bifurcates towards a periodic solution. Using the normal form theory and center manifold argument, the explicit formulae which determine the stability, the direction and the periodic of bifurcating period solutions are derived. Numerical simulations are carried out to explain the mathematical conclusions.     

金属硫蛋白加质子常数及与C_d(Ⅱ)络合常数测定

用pH计和Cd离子选择电极测定了金属硫蛋白的加质子常数及其与Cd(Ⅱ)的络合常数,用改进的简化络合模型处理实验结果,得到了去金属硫蛋白(apo MT)中6类不同的加质子基团的数目及其加质子常数。对Cd(Ⅱ)滴定数据的计算表明,MT中两个结构域——α和β对Cd(Ⅱ)的络合常数相差约1000倍。从热力学定量描述了MT中两个结构域结合金属离子选择优先顺序。     

Bi系超导体原始粉末的化学吸附行为

用傅氏变换红外光谱（FTIR）研究了不同方法制备的Bi系超导体原始粉末研磨过程中；自环境气相中的化学吸附行为．结果表明；在空气中研磨，粉末化学吸附空气中的CO2和H2O在氩气中研磨则无化学吸附现象．用Bi系超导体晶体结构的特征分析了吸附机理.     

Probing local and long-range structure simultaneously: an in situ study of the high-temperature phase transition of alpha-AlF3

We show in this Communication that the combination of Rietveld and pair distribution function (PDF) analyses allows unique insight into the nature and driving force of the phase transition of alpha-AlF3, which was not available from conventional structural analysis methods alone. The use of image plate technology allows structural changes to be followed in "real time" and reduces the time required to collect high-resolution PDF data from hours (with a conventional solid state detector) to seconds. This methodology produces raw data that can simultaneously be analyzed by both Rietveld and PDF analysis.     

Inter-DNA attraction mediated by divalent counterions

Can nonspecifically bound divalent counterions induce attraction between DNA strands? Here, we present experimental evidence demonstrating attraction between short DNA strands mediated by Mg2+ ions. Solution small angle x-ray scattering data collected as a function of DNA concentration enable model independent extraction of the second virial coefficient. As the [Mg2+] increases, this coefficient turns from positive to negative reflecting the transition from repulsive to attractive inter-DNA interaction. This surprising observation is corroborated by independent light scattering experiments. The dependence of the observed attraction on experimental parameters including DNA length provides valuable clues to its origin.     

Pd/SiC催化碘代芳烃和芳基硼酸羰化Suzuki偶联反应性能

以高比表面积碳化硅为载体,通过液相还原法制备出Pd/SiC催化剂,并用于催化碘代芳烃和芳基硼酸羰化Suzuki偶联反应.利用X射线衍射、电感耦合等离子体质谱和高分辨透射电子显微镜等对催化剂进行了表征.结果表明, SiC表面的Pd纳米颗粒分散均匀,平均粒径约为2.8 nm.在优化溶剂、碱、压力和温度等反应条件后,发现以3 mmol的K2CO3和10 mL苯甲醚分别为碱和溶剂,1.0 mmol碘苯和1.5 mmol苯硼酸在3 wt% Pd/SiC催化剂存在的条件下,在CO压力为1.0 MPa和100oC下反应8 h即可实现羰化偶联,碘苯转化率为90%,二苯甲酮选择性为99%.并且, Pd/SiC对含有不同官能团的碘代芳烃和芳基硼酸羰化Suzuki偶联反应具有较好的普适性.同时, Pd/SiC也具有较好的稳定性,经5次循环反应后,碘苯转化率从90%降至76%;催化剂活性降低的主要原因是活性组分Pd在有机反应体系中的流失.     

钢框架-混凝土剪力墙混合结构连续化计算方法

提出了钢框架-混凝土剪力墙混合结构体系的一种连续化的计算方法，该方法考虑了这种结构中钢框架部分节点柔性连接，推导了考虑节点柔性连接时，钢框架-混凝土剪力墙混合结构中钢框架部分的层抗侧刚度．     

A new azaphilone from the entomopathogenic fungus Hypocrella sp.

This report describes the isolation of a new azaphilone, designated hypocrellone A (2), together with five known compounds (1, 3–6) from a submerged culture of the entomopathogenic fungus Hypocrella sp. (isolate WYTY-21). The absolute stereostructures of the two compounds (1 and 2) were elucidated based on 1D and 2D NMR spectroscopic and mass spectrometric data combined with the data from various chemical transformations. Hypocrellone A (2) and three (3–6) of the five known compounds were cytotoxic to hepatoma cells (cell line BEL-7404); IC₅₀ values ranged from 6.2 to 17.4 μM. At 200 μM, none of the six compounds was toxic to normal human liver cells (cell line HL-7702) or to normal human kidney epithelial cells (cell line HEK-293T).     

Some Characterizations of Left Weakly Regular Ordered Semigroups

In this paper, the notion of left weakly regular ordered semigroups is introduced. Furthermore, left weakly regular ordered semigroups are characterized by the properties of their left ideals, right ideals and (generalized) bi-ideals, and also by the properties of their fuzzy left ideals, fuzzy right ideals and fuzzy (generalized) bi-ideals.     

前言

放射化学是研究放射性物质及其辐射效应的一门化学分支学科。现代放射化学主要包括核能放射化学、环境放射化学、放射性药物化学、放射分析化学、放射性元素化学及核化学等。 放射化学是19世纪末随着放射性和放射性核素的发现而诞生的一门学科。正由于核化学和放射化学的贡献, 发现了核裂变现象,从而开创了核科学时代的到来。近年来,核化学和放射化学的发展已经为国家安全、 社会和经济进步、 能源需求、人类健康、环境保护以及科学发展等做出了巨大贡献。例如在基础科学方面,与核物理学家合作将元素周期表扩展了近1/3,提出了锕系理论等。全世界现有能源的1/6来自核能, 全球具有一定规模的医院都设有核医。放射化学的特点表明,它不仅是一种重要的和不可取代的核方法,而且是一门极具生命力的前沿科学。放射化学的三大推动力是：国家需求, 基础研究, 学科交叉。它不仅蕴含着大量既有重要科学意义、又能满足国家重大需求的科学问题,而且与其他学科交叉,产生了许多新的学科生长点。