UV-B辐射增强对褶皱臂尾轮虫实验种群动态的影响

采用单个体培养和生命表技术，研究了不同UV—B辐射剂量对褶皱臂尾轮虫（Brachionus plicatilis）实验种群的存活时间、产卵饿、生殖率和内禀增长率等关键种群参数的影响．结果表明，UVB辐射可使轮虫的存活时间显著缩短（p〈0．05），对照组轮虫存活时间最长，在本文验条件下达390h；最大剂量1．20kJ／m^2处理组最短，为300h．低剂量的0．24、0．48和0．72kJ／m^2 UV—B辐射促进了褶皱臂尾轮虫的繁殖，而高剂量的0．96和1．20kJ／m^2 UV—B辐射抑制了褶皱臂尾轮虫的繁殖．褶皱臂尾轮虫的生命期单随UV—B辐射剂量的增大呈一致性缩短，可以作为大气UV—B辅射强弱的生物指标．     

手性胶束中的有机反应—— Ⅷ.手性胶束中的不对称Darzens缩合

本文报道ω-溴代苯乙酮与各种芳醛在手性表面活性剂N,N-二甲基-N-十二烷基麻黄素溴化铵及N,N-二甲基-N-十六烷基麻黄素溴化铵形成的手性胶束水溶液中的不对称Darzens缩合反应,得到手性α,β-环氧酮,对映体过量值最高达11.9%.     

Chemisorption of CO and mechanism of CO oxidation on supported platinum nanoclusters

Kinetic, isotopic, and infrared studies on well-defined dispersed Pt clusters are combined here with first-principle theoretical methods on model cluster surfaces to probe the mechanism and structural requirements for CO oxidation catalysis at conditions typical of its industrial practice. CO oxidation turnover rates and the dynamics and thermodynamics of adsorption-desorption processes on cluster surfaces saturated with chemisorbed CO were measured on 1-20 nm Pt clusters under conditions of strict kinetic control. Turnover rates are proportional to O(2) pressure and inversely proportional to CO pressure, consistent with kinetically relevant irreversible O(2) activation steps on vacant sites present within saturated CO monolayers. These conclusions are consistent with the lack of isotopic scrambling in C(16)O-(18)O(2)-(16)O(2) reactions, and with infrared bands for chemisorbed CO that did not change within a CO pressure range that strongly influenced CO oxidation turnover rates. Density functional theory estimates of rate and equilibrium constants show that the kinetically relevant O(2) activation steps involve direct O(2)* (or O(2)) reactions with CO* to form reactive O*-O-C*=O intermediates that decompose to form CO(2) and chemisorbed O*, instead of unassisted activation steps involving molecular adsorption and subsequent dissociation of O(2). These CO-assisted O(2) dissociation pathways avoid the higher barriers imposed by the spin-forbidden transitions required for unassisted O(2) dissociation on surfaces saturated with chemisorbed CO. Measured rate parameters for CO oxidation were independent of Pt cluster size; these parameters depend on the ratio of rate constants for O(2) reactions with CO* and CO adsorption equilibrium constants, which reflect the respective activation barriers and reaction enthalpies for these two steps. Infrared spectra during isotopic displacement and thermal desorption with (12)CO-(13)CO mixtures showed that the binding, dynamics, and thermodynamics of CO chemisorbed at saturation coverages do not depend on Pt cluster size in a range that strongly affects the coordination of Pt atoms exposed at cluster surfaces. These data and their theoretical and mechanistic interpretations indicate that the remarkable structure insensitivity observed for CO oxidation reactions reflects average CO binding properties that are essentially independent of cluster size. Theoretical estimates of rate and equilibrium constants for surface reactions and CO adsorption show that both parameters increase as the coordination of exposed Pt atoms decreases in Pt(201) cluster surfaces; such compensation dampens but does not eliminate coordination and cluster size effects on measured rate constants. The structural features and intrinsic non-uniformity of cluster surfaces weaken when CO forms saturated monolayers on such surfaces, apparently because surfaces and adsorbates restructure to balance CO surface binding and CO-CO interaction energies.     

A New Luminescent Ruthenium(II) Polypyridine‐derived Dipicolylamine Complex as a Sensor for Cu2+ Ions

A chemo‐sensor [Ru(bpy)₂(bpy‐DPF)](PF₆)₂ ( 1 ) (bpy=2,2′‐bipyridine, bpy‐DPF=2,2′‐bipyridyl‐4,4′‐bis(N,N‐di(2‐picolyl))formylamide) for Cu²⁺ using di(2‐picolyl)amine (DPA) as the recognition group and a ruthenium(II) complex as the reporting group was synthesized and characterized successfully. It demonstrates a high selectivity and efficient signaling behavior only for Cu²⁺ with obvious red‐shifted MLCT (metal‐to‐ligand charge transfer transitions) absorptions and dramatic fluorescence quenching compared with Zn²⁺ and other metal ions.     

On SS-Quasinormal Subgroups of Finite Groups

A subgroup of a group G is said to be Sylow-quasinormal (S-quasinormal) in G if it permutes with every Sylow subgroup of G. A subgroup H of a group G is said to be Supplement-Sylow-quasinormal (SS-quasinormal) in G if there is a supplement B of H to G such that H is permutable with every Sylow subgroup of B. In this article, we investigate the influence of SS-quasinormal of maximal or minimal subgroups of Sylow subgroups of the generalized Fitting subgroup of a finite group.     

高速弓网系统动力学参数敏度分析及优化

随着高速列车运行速度的提升, 弓网关系这一基础力学问题备受关注. 良好的弓网关系是确保列车安全高效运行、稳定可靠受流、降低接触线与受电弓滑板磨耗等的基本前提. 其中, 受电弓和接触网的动力学参数对弓网耦合作用起至关重要的作用. 本文采用弓网接触力随机统计特征作为优化目标函数,进行受电弓动力学参数的敏度分析和优化设计. 首先, 建立了二维弹性链悬挂接触网-三质量块受电弓动力学模型,根据EN50318: 2018标准验证了动力学建模和分析结果的正确性. 然后, 基于高速弓网系统的动力学仿真, 进行了DSA380型高速受电弓三质量块参数的动力学敏度分析, 确定了9个动力学参数的敏感度级别, 弓头等效质量敏度评级最高,下框架等效阻尼次之, 下框架等效质量和上框架等效阻尼第三. 最后, 研究了弓头等效刚度和等效阻尼联合变化对弓网耦合动力学性能的影响,给出了提升弓网耦合性能的弓头双参数优化方案, 建议同时减小弓头等效阻尼和增大弓头等效刚度, 能够实现比单参数优化更好的弓网耦合性能.      

纳米尺寸二硫化钼的制备与应用研究进展

二硫化钼(MoS₂)作为一种与石墨烯具有类似结构的材料, 近些年来受到了科学家们的越来越多的关注. 它凭借自身的层状结构, 独特的电子学、电化学性质, 大的比表面积以及表面改性的潜能, 在许多领域都有着广泛的应用. 本文简单论述了目前纳米尺寸MoS₂的制备方法, 包括微机械剥离、液相剥离、嵌锂法、水热反应、气相沉积以及热分解法等, 并对这些方法在制备纳米MoS₂中具备的优点和存在的不足作了简单点评. 另外, 介绍了纳米MoS₂在光电子器件、催化、传感、能量存储与转化等领域的应用研究进展, 并着重介绍了其在电化学和生物传感分析方面的应用研究现状, 并对未来纳米MoS₂的重点研究方向作出了展望. 从目前的研究来看, 纳米MoS₂在器件、能量存储和传感分析等应用方面存在着巨大的潜质, 有望成为一种继石墨烯之后性能十分优良的多功能材料.     

2015年度力学科学处基金项目受理情况介绍

介绍了2015 年度国家自然科学基金委员会数理科学部力学科学处受理的面上项目、青年科学基金项目、地区科学基金项目、重点项目、优秀青年科学基金、国家杰出青年科学基金和海外及港澳学者合作研究基金项目的申请情况.      

人眼晶状体调节机制和力学

晶状体是人眼屈光系统的核心,其视觉调节过程由睫状肌、悬韧带和晶状体共同实现:通过睫状肌牵引悬韧带运动,引起晶状体变形(变凸或扁平),从而改变眼睛的屈光力,使得眼睛聚光的焦点准确地落在视网膜上,最终产生视觉.晶状体的视觉调节从本质上说是一个力学问题,调节过程的实现与视觉质量紧密相关;同时调节机制也是最常见的眼部老化退行性疾病--老视的核心问题.本文介绍了晶状体调节的各种理论假说及其发展,并概述了晶状体的力学性能.     

一种水稻愈伤组织特异性启动子的克隆及其应用

筛选标记基因是一种用于植物遗传转化后阳性转化子筛选的有效手段,但目前介导标记基因表达均采用组成性启动子.这些启动子虽然在植物遗传转化得到了广泛应用,但由于是组成性表达,在转基因的生物安全性存在标记基因的安全性担忧.为了克服这一缺点,本文从水稻基因组内克隆了水稻半胱氨酸蛋白酶基因(Cyctein protease,CP)的启动子,通过gus转基因的验证,该启动子只在愈伤组织表达,不在水稻根、茎、叶等组织表达,为愈伤组织特异性表达启动子(Callus-specific Promoter,CSP).将该启动子用于介导筛选性标记基因的表达,通过对筛选性标记基因潮霉素磷酸转移酶基因(hpt)的密码子优化,明显提高了CP启动子在水稻转基因选择的转化效率,质粒转化效率和阳性植株率均达到了pCAMBIA1301的35S启动子介导标记基因hpt的选择效果.