基于分子动力学模拟的天然橡胶黏弹性材料力学行为

以天然橡胶为例,采用分子动力学模拟方法,研究了单轴拉伸条件下材料分子链聚合度参数p、环境温度T和加载率R对黏弹性材料力学性能的影响.结果 表明,材料应力随分子链聚合度和加载率的增加而增加,随温度的升高而降低,低温高频下材料呈现出塑性特点.在R=108 s-1,T=250 K的条件下,p=20,40时,材料应力峰值分别为...     

蚕豆子叶愈伤组织的生长与分化

利用蚕豆(Vicia faba)未成熟种子的幼龄子叶为外植体,以MSB_5为基本培养基,可较好的克服蚕豆组织和细胞培养中遇到的诱导率低、生长缓慢、褐化死亡等困难。第一代或继代一次的蚕豆幼龄子叶的愈伤组织可分化出幼芽和根。继代两次以上的愈伤组织则失去分化能力,但仍能继代培养,现已继代培养两年之久,可作为植物细胞工程的原始材料加以利用。     

由三倍体西瓜下胚轴诱导植株再生的研究

将三倍体西瓜(Citrullus Vul(?)aris Schrad。)下胚轴切段接种在添加0.02mg/L2,4-D和0.6mg/L6BA的MS培养基上,可诱导出生长旺盛、结构致密的愈伤组织.将愈伤组织转移到含不同浓度的6BA、IAA、IBA和三十烷醇的分化培养基上,分化出了芽和根,进而长成了正常的植株.将不定芽接种在含0.2～0.4mg/L6BA和6mg/L维生素P_1的MS培养基上.可得到许多簇生芽和植物体.用蛭石代替琼脂的生根培养基对于根系的生长和试管苗的移植有良好的效果.经细胞学观察表明,由三倍体西瓜下胚轴诱导出再生植株的染色体倍性有所变化,即有一倍体(n=11)、二倍体(2n=22),三倍体(3n=33)和非整倍体等.     

灰色控制系统的极值白化最优控制

本文提出了灰色控制系统极值白化最优控制的概念.对于灰色线性二次问题给出了极值白化最优控制存在的条件,性能指标的估计以及在极值由化最优控制反馈下系统的稳定性分析.     

Light-induced helix formation

This study shows that incorporation of [Rub2m-OH]2+ at the N-terminus of the Fs peptide enhances its stability by approximately 0.15 kcal/mol through the mechanism of dipole-dipole coupling at the excited state, suggesting that photoinduced charge generation at a well-controlled and specific location provides a convenient means to trigger helix-coil transition on nanosecond or even faster time scales.     

一类混合概率型算子的任意阶矩

利用Γ函数在区间[0, ∞]上给出了一类加权积分型算子并得到其各阶矩，推广了关于SzaszDurrmeyer算子及Baskakov-Durrmeyer算子的相应结果，同时指出了它在研究随机过程中的意义。     

料丝自加压式挤出机加料段不溢料条件分析

借助未熔丝材的活塞作用,部分熔融沉积造型(FDM)技术靠料丝插入的驱动力将熔融材料挤出.在分析加料段中熔融物料流变特点的基础上,找出确保熔融物料不会从料丝插入口间隙处溢出的三个影响因素(P/z、表观粘度ηa和料丝半径r0),得出料丝插入速度VS应当大于临界速度VS0.     

Pore structure of “sivol”

Small-angle x-ray scattering has been used in an investigation of the pore structure of sivol, a material prepared by thermochemical treatment of chrysotile asbestos. It has been shown that sivol has a well-developed pore structure. Pore size distribution curves have been obtained, showing a maximum with a radius of gyration R=2.5–3.0 nm. The data from small-angle scattering are in good agreement with results obtained in previous calculations based on adsorption measurements (for R 2.5 nm). It has been shown that some of the finest pores are not accessible for the molecules being adsorbed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 978–981, May, 1990.     

Nanoscopic surface patterns of diblock copolymer thin films

The surface topography of thin diblock copolymer films is studied by atomic force microscopy (AFM). With AFM an island-to-ribbon transition is observed for symmetric polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) on mica with increasing solution concentration. Our study also demonstrates how the formation of the pattern strongly depends on the copolymer composition based on the volume fraction. The substrate and solvent used both have great effects on the morphology of the thin films. Only by using highly polar substrate (mica), can we gain regular pattern. The reason why the regular islands cannot be obtained with symmetric PS-b-P4VP on graphite is also explained. On mica using nonselective and selective solvents, a rather regular pattern can be obtained. The difference is only in the solution concentration for forming regular patterns.     

Electronic stability of magnetic Fe/Co superlattices with monatomic layer alternation

We report a surprising observation that the growth of the [Fe(1 ML)/Co(1 ML)](n) superlattice of L1(0) structure on Cu(100) is stable only up to six atomic layers (n=3), which cannot be rationalized by stress arguments. Instead, first-principles calculations reveal a transition from the L1(0) to the B2 structure due to the effect of dimensionality on the stability of the electronic structure of the superlattice. Whereas the majority-spin electrons are energetically insensitive to the layer thickness, the minority-spin electrons induce the transition at n=3.