负泊松比材料和结构的研究进展

负泊松比材料和结构具有特殊的力学性能,在单轴压力(拉力)作用下发生横向收缩(膨胀).其在抗剪承载力、抗断裂性、能量吸收和压陷阻力等方面比传统材料更有优势,因而负泊松比材料在医疗设备、传感器、防护设备、航空航海及国防工程等领域有广泛的应用前景,但目前负泊松比材料的应用与普及仍面临一些挑战.本文广泛讨论了国内外关于负泊松比材料的研究成果并介绍了负泊松比材料的最新进展,将负泊松比材料大体概括为以下4类:天然负泊松比材料、胞状负泊松比材料、金属负泊松比材料、多重和复合负泊松比材料.主要介绍了各种负泊松比材料的内部结构、负泊松比机理、力学性能以及在各行各业的新发明、新应用.针对目前负泊松比材料研究理论和实验成果多,而实际应用仍然较少的情况,指出了负泊松比材料的缺点及其推广所面临的挑战.目前负泊松比材料面临的主要问题是制造成本高、孔隙率大而承载力不足以及仅适用于小应变情况等.本文针对此情况详细介绍了金属负泊松比材料及其设计和制作的方法,改善负泊松比材料的不足并推广其应用.      

Synthesis and characterization of diselenide crosslinked polymeric micelles via Diels–Alder click reaction

ABSTRACT

A well-defined amphiphilic block copolymer, poly (ethylene oxide)-b-(poly (furfuryl methacrylate) (PEO-b-PFMA) was prepared by single electron transfer living radical polymerization using tris(dimethylamino)ethyl amine (Me6TREN) as a ligand. The block copolymer formed sub-100 nm micelles in water with PEO as a shell and PFMA as a core. Diels–Alder click type reaction was employed to form core-crosslinked micelles using a diselenide-containing crosslinker without any catalyst. The block copolymer and micelles were characterized by gel permeation chromatography, nuclear magnetic resonance, Fourier-transform infrared spectroscopy, dynamic light scattering analysis and transmission electron microscopy. The stability of core-crosslinked micelles under reductive-oxidative condition was also investigated. The diselenide crosslinked micelles displayed good stability against extensive dilution but decomposed under the presence of hydrogen peroxide or glutathione. The redox responsive core-crosslinked micelles can be a promising carrier for drug delivery applications.     

爱因斯坦黎曼流形的全脐超曲面

本文研究爱因斯坦黎曼流形的全脐超曲面,给出它为全测地的或常曲率的充分条件。也研究全测地超曲面。     

氟尿嘧啶自旋标记衍生物的合成与抗肿瘤活性

稳定氮氧自由基作为某些抗癌药物的载体,不仅能提高药物对癌细胞的选择性,而且为借助电子自旋共振(ESR)技术研究药物的作用机理和代谢提供了一种新手段。在前文中,我们报道了几种5-氟尿嘧啶的自旋标记衍生物。作为这一工作的继续,本文报道一系列新的氟尿嘧啶自旋标记衍生物10_(a—c)、11_(a—c)和12_(a—c)的合成及其抗肿瘤活性的研究。     

Simulations of Sol-to-Gel Modeling: Effects of Mobility,Reversibility, and Quality of Solvent

Some of our recent work on computer simulation modeling of the sol-to-gel transition for the polymerization by step reaction are presented. Depending on the variants of the model, a random distribution of bifunctional and tetrafunctional monomers of concentration C₂ and C₄ respectively, and their chains (bond-fluctuating) are used as primary reacting units on a simple cubic lattice as the initial sol-phase. Effects of solvent, temperature, mobility of monomers, rate of reaction, and reversibility are considered in understanding the evolution of microgels, onset of gelation and the nature of sol-to-gel transition, inhomogeneity, etc. Gel point (p_c, gel volume fraction (P_G), weight average degree of polymerization (M_W), structure factor (S(q, t)) show various interesting variations with the conversion factor (p). For example, sol-to-gel transition seems nonuniversal with respect to quality of the solvent, degree of inhomogeneity depends on the quality of solvent and rate of reaction due to interplay between the phase-separation and cross-linking.     

Triterpenoid Saponins from Clematis tangutica

Clenlall\vlanglllica(Maxim).KorshisaTibetanherbandhasbeenusedtotreatindigestionandskindiseasesl.Nophytochemicalworkonthisplanthasbeenreportedinliterature.Inourwork.someglycosideswereobtainedtyomaerialpartofthisplant.Inthispaper.thestructureelucidationoftwonewtriterpenoidsaponins.tanguticosideAandBaredescribed.Onmineralacidhydrolysis.both1and2yieldedthesameaglycone.BycomparingMP.MS,'HNMRand13CNMRspectratheaglyconewasdeterminedtobehederagenin=.Glucoseandrhamnosewereobtainedfromhydrolysis…     

二阶积分-微分方程的Numerov迭代解法

本文以二阶齐次常微分方程的Numerov格式为出发点,构造了二阶积分-微分方程和二阶积分-微分方程组的迭代求解格式,比直接解法(高斯全主元消去法)不但大大节约了计算机的存贮量,而且也大大节约了计算时间。     

近似评价函数确定运动极限及其在形状优化中的应用

针对二维连续体形状优化过程中解析灵敏度求解困难的情况,利用响应面方法将目标函数和约束函数近似显式化,建立序列二次规划模型。为了保证优化模型的可靠性,结合试验设计方法,以较少的结构分析代价构造约束响应面,从而能够快而稳定地收敛,本文重点研究并建立了二次近似评价函数用以计算自适应运动极限的策略。算例说明这种策略是有效而稳定的。     

关于集值条件期望和本性上确界

本文首先讨论集值随机变量族本性上确界和集值条件期望运算的交换性;其次给出集值条件期望族本性上确界的轶性质.     

邻硝基苯基荧光酮-氯代十六烷基吡啶双波长增敏法测定微量铁(Ⅲ)

在ＨＡＣ－ＮａＡＣ缓冲体系中,邻硝基苯基荧光酮、氯代十六烷基吡啶与铁形成三元络合物。试剂的最大吸收为５３０ｎｍ,络合物的最大吸收为６４４ｎｍ,用双波长增敏法测得表观摩尔吸光系数为５５×１０４络合物的组成比为１∶１∶１,铁量在０～６μｇ／２５ｍＬ符合比