Models and the dynamics of theory-building in physics. Part I—Modeling strategies

A deeper understanding of models is sought in considering what models do, rather what they are. This distinction emphasizes how two different modeling strategies, as they pursue different purposes, do invest in different options, in particular in regard to rigor and immediate empirical relevance. The analysis focuses therefore on the services expected from models by the scientists who construct them: models are sought for how they contribute to exploring and testing the context in which they operate. In a forthcoming Part II these general considerations will be anchored in the presentation of specific case studies.     

KBe_2BO_3F_2的晶体角度调谐

基于三波耦合的能量、动量守恒条件和KBe2BO3F2(KBBF)晶体最新的色散方程,研究了共线Ⅰ类、Ⅱ类相位匹配和非共线Ⅰ类相位匹配KBBF晶体的角度调谐曲线;并比较了共线相位匹配和非共线相位匹配的特点.     

超临界平面耦合轴向运动梁的静平衡分岔

运用数值方法研究固定边界条件下,超临界速度范围内的轴向运动梁横向与径向耦合平面的静态平衡位形分岔行为,其中轴向运动梁的静态平衡位形包括直线形状的0解,以及随传输速度分岔得到的曲线形状的非平凡分岔解.在梁的两端固定的边界条件下,运用有限差分法对轴向运动梁平面耦合非线性方程以及对应于非线性平面耦合方程的静态平衡方程作数值解.以铜材料的梁为例,数值求解轴向运动梁耦合平面的静平衡非平凡解,并仿真分析了系统参数对非平凡分岔解的影响.     

市政污水厂污水和污泥中15种典型抗生素同步测定方法优化

采用固相萃取/超声辅助萃取-超高效液相色谱-质谱联用技术,建立了一种适用于市政污水厂污水和污泥中15种典型抗生素的同步测定方法.污水样品经过滤、酸化及固相萃取柱富集净化;污泥样品用体积比为3 ∶ 1的McIlvaine缓冲液-乙腈和Mg( NO3 )2-NH3·H2 O超声提取后经固相萃取柱富集净化.以体积分数为0. ...     

下穿已有隧道泥水盾构施工的预测分析

基于2010年上海世博会重大配套工程——打浦路隧道复线工程,结合具体实际地质条件及施工参数,利用Abaqus有限元分析软件,建立三维非线性有限元模型,模拟泥水盾构沿弧线斜下穿已有隧道的施工过程.计算并分析在泥水盾构施工过程中,已有隧道发生的变形、产生的应力以及地表发生的沉降,预测泥水盾构施工对已有隧道和地表的影响,并与实测数据进行比较,说明分析预测的可信性.所得结果不仅对该工程具有积极的指导意义,而且对其他类似工程的分析也具有重要的借鉴作用.     

Recent results on hydrogen and hydration in biology studied by neutron macromolecular crystallography

Neutron diffraction provides an experimental method of directly locating hydrogen atoms in proteins, a technique complimentary to ultra-high-resolution [1, 2] X-ray diffraction. Three different types of neutron diffractometers for biological macromolecules have been constructed in Japan, France and the United States, and they have been used to determine the crystal structures of proteins up to resolution limits of 1.5-2.5 A. Results relating to hydrogen positions and hydration patterns in proteins have been obtained from these studies. Examples include the geometrical details of hydrogen bonds, H/D exchange in proteins and oligonucleotides, the role of hydrogen atoms in enzymatic activity and thermostability, and the dynamical behavior of hydration structures, all of which have been extracted from these structural results and reviewed. Other techniques, such as the growth of large single crystals, the preparation of fully deuterated proteins, the use of cryogenic techniques, and a data base of hydrogen and hydration in proteins, will be described.     

基本蚁群算法的A.S.收敛性研究

蚁群算法是近几年优化领域中新出现的一种启发式仿生类并行智能进化算法，虽然该算法已经在众多组合优化领域中得到广泛应用，但是对其收敛性尤其是A．S．（AlmostSurely）收敛性问题的研究还存在很多空白．本文在介绍蚁群算法基本原理的基础上，以Markov链和离散鞅作为研究工具，对基本蚁群算法的A．S．收敛性问题进行了理论证明，把最优解集序列转变为下鞅序列来考察残留信息素轨迹向量的收敛性，随后提出了基本蚁群算法首达时间的定义，并对基本蚁群算法首次到达时间的期望值进行了理论分析．     

Label-free selective sensing of Pb2+ lead(II) sensors based on the aggregation of a pyrene fluorescent probe

In the present work, we report a label-free fluorescence turn-on approach for the sensitive and selective sensing of Pb²⁺. Pyrene with one positive charge was used as the fluorescent probe, and thrombin aptamer (TBA), which was a G-rich oligonucleotide, was employed to form G-quadruplex with lead(II). When TBA and Pb²⁺ were mixed with lead(II) in an aqueous solution, it was folded into a stable G-quadruplex. Subsequently, a single-stranded nucleic acid-specific nuclease S1 was added. The G-quadruplex stabilized by Pb²⁺ lead(II) had markedly a significant resistant ability to nuclease S1 digestion. However, in the absence of Pb²⁺ lead(II), no quadruplex or less stable quadruplex was formed and TBA was digested by nuclease S1 in 3 min under the optimized experimental conditions. Finally, pyrene probe was mixed with oligonucleotide in Pb²⁺ lead(II). Electrostatic interactions between oligonucleotide (a polyanion) and the probe induced the aggregation of the probe, which in turn produced strong emission of the strong pyrene excimer emission. The intensity of the induced excimer emission was directly proportional to the amount of Pb²⁺ added. Our approach shows good selectivity and sensitivity for the detection of Pb²⁺ with a limit of detection limit as low as 800 nmol/L.     

系列羟基苯基卟啉在碱体系中的性质

利用紫外-可见光谱、拉曼和红外光谱研究系列羟基苯基卟啉在碱体系中的性质.结果表明,碱与羟基苯基卟啉周边的羟基发生反应形成盐,而与卟啉中心环上的H没有相互作用,说明羟基苯基卟啉分子的中心环比较稳定,电荷主要分布在周边meso-位的取代基上,该位置易发生反应.     

The radiolytic behavior and mechanism of calixarene crown ether under γ-irradiation

Bis(2-propyloxy)calix[4]crown-6 (BPC6) is an effective separation agent for cesium removing from spent nuclear fuel. The study on radiolytic behavior of BPC6 itself under γ-irradiation was required for evaluating its feasibility of practical application. It was found that BPC6 exhibited excellent radiation stability at dose less than 100 kGy. However, the isopropyl groups in BPC6 under- went oxidation and dealkylation to form carbonyl groups and phenolic hydroxyl groups at dose above 300 kGy, respectively. When the dose was more than 1000 kGy, the ring opening of crown ether structure of BPC6 resulted in the formation of phenolic hydroxyl groups as well. The formation of radiolytic products containing phenolic hydroxyl groups during the irradiation of BPC was confirmed by using FeCl 3 as a probe. Combining with the radiolytic behavior of two model chemicals (1-isopropoxybenzene and benzo-18-crown-6 ether), the radiolytic behavior and mechanism of BPC6 under -irradiation was testified further.