Oriented noncrystalline structure in PET fibers prepared with threadline modification process

The development of an oriented noncrystalline phase in a semicrystalline polymer filament has been studied via X-ray scattering. These unique PET fibers contain a relatively high noncrystalline content and also have high tenacity, high modulus, and low breaking elongation. Fiber properties were found to be very responsive to the oriented amorphous phase content. This phase was utilized for interpreting noncrystalline orientation in PET fibers produced by a new extrusion technique. Here, the oriented noncrystalline regions in a series of PET fibers varies from 6% to 63%, depending strongly on the production conditions. In particular, samples produced with a newly developed threadline modification process possess a high content of oriented noncrystalline polymer. Measurements such as dynamic and static mechanical properties have been performed on various samples, and these properties are related to the oriented noncrystalline phase. The results provide direct evidence for the existence of highly oriented noncrystalline material in these unique PET fibers spun with a threadline modification process. © 1996 John Wiley & Sons, Inc.     

Anisotropy of hole structures in oriented polycarbonate probed by two-dimensional angular correlation of annihilation radiation

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) experiments have been performed on an uniaxially oriented polymer, bisphenol-A polycarbonate. The two-dimensional hole structures of unoriented and oriented polymers, determined from the momentum distributions, are found to be spherical and ellipsoidal, respectively. The average hole radii are determined to be 2.9 Å in the unoriented sample and between 2.3 and 3.8 Å in the oriented sample. Applications of the 2D-ACAR method to image the three-dimensional hole structures of polymeric materials are discussed. © 1996 John Wiley & Sons, Inc.     

超拉伸聚乙烯的弹性模量和导热性能

为了揭示聚合物分子链伸展、取向的本征特性，发展了两个新的测量方法和实验装置，用于研究拉伸比高达２００的超拉伸聚乙烯凝胶的弹性性能、传热性能和聚合物结构的关系．应用激光脉冲热致超声法给出材料拉伸方向和横向杨氏模量，应用激光脉冲光热辐射法给出拉伸方向，横向和厚度方向的导热系数．随拉伸比λ的增加，轴向杨氏模量急剧的增加，而横向的仅有少许减小．导热系数具有相似的特性．本文发现当λ＝２００时，这种拉伸取向聚乙烯的轴向模量可达钢的８０％，而导热系数甚至可达２倍，直至成为热的良导体，这是由于在高拉伸比时形成了相当数量的伸展分子链构成的针状晶体———晶桥．本文提出晶桥作为短纤维分散相的取向聚合物的结构模型，对于超拉伸聚乙烯的上述特性可以进行统一描述和定量化分析，和实验结果很好符合．     

γ-AlOOH纳米棒的水热合成与形貌调控

γ-AlOOH作为液相法合成γ-Al₂O₃的前驱体,其形貌与最终产物的性能密切相关。 本文采用水热法合成γ-AlOOH纳米棒,通过改变Al³⁺浓度和沉淀剂的种类调控γ-AlOOH纳米棒的长径比,利用X射线衍射仪(XRD)和透射电子显微镜(TEM)表征产物的晶体结构和形貌。 结果表明,随Al³⁺浓度增大可得到长径比在5.9~8.0的γ-AlOOH纳米棒,而改变沉淀剂的种类可进一步将长径比增大到8.0~10.0。 通过对产物结晶过程的分析,发现增大Al³⁺浓度和增强沉淀剂碱性均可以促进铝离子与羟基的配合。 提高反应体系中Al(OH)₃浓度,有利于γ-AlOOH晶粒的成核,促进了晶核之间的定向接触,从而提高了纳米棒的长径比。 长径比为10.0的γ-AlOOH纳米棒烧结所得纳米γ-Al₂O₃改性变压器油(体积分数为0.1%)的正冲击击穿强度较纯油提高9.9%.     

三类有向三元系之间关系的一种猜想

一个Mendelsohn (Directed, 或Hybrid)三元系 MTS$(v, \lambda)$~(DTS$(v, \lambda)$,或HTS$(v,\lambda))$, 是由$v$元集$X$ 上的一些循环（可迁,或循环和可迁）三元组(简称区组)构成的集合${\cal B}$, 使得$X$上每个由不同元素组成的有序对都恰在 ${\cal B}$的$\lambda$个区组中出现.本文主要讨论了这三类有向三元系之间的一种关联关系,给出猜想：任意MTS$(v,\lambda)$的区组关联图$G(\     

The Crystallization of Poly (3-dodecyltbiophene) in an Oriented Solidification Environment

Poly (3-alkylthiophenes) (P3ATs) have made up of a family of conductive polymerswhich are soluble, fusible and processable, since the introduction of flexible alkyl sidechains"'. It is generally accepted that P3ATs can form similar layered structures. inwhich the thiophene rings possess planarity and the side chains act as spacers'-'. Whenthe number. of 'carbon atoms of alkyl side chains is more than 10, some orderlyarrangements will occur for side chains betWeen the' layers'. It has been w…     

On Percolation with Fibers or Layers

We consider site percolation on Z ^d, directed edges going from any sZ ^d to s+A ₁,..., s+A _n, where A ₁,..., A _n are the same for all sites and at least two of them are noncollinear. A site is closed if it belongs to p+Block, where p is a point in a Poisson distribution in R ^dZ ^d with a density and Block={sL: |s|M}+{sR ^d: |s|}, where L is a linear subspace of R ^d, |·| is the Euclidean norm, =max(|A ₁|,..., |A _n|) and M is a parameter. We study the behavior of *, the critical value, and P _closed*, corresponding critical percentage of closed sites, when M. Denote R ^d/L the factor space. Call two nonzero vectors U, V codirected if U=kV, where k>0. Theorem. If there are A _i and A _j whose projections to R ^d/L are not codirected, then *1/M ^dim(L) and P _closed* remains separated both from 0 and 1 when M. If projections of all A ₁,..., A _n to R ^d/L are codirected, then *1/M ^dim(L)+1 and P _closed*1/M when M.     

基于面向对象技术的多媒体CAI素材库系统

建立实用、高效的多媒体ＣＡＩ素材库是高效率、高质量开发ＣＡＩ软件的基础和关键．本文从数据模型、面向对象分析和存储模式三方面入手,提出一种支撑ＣＡＩ制作工具的素材库体系结构,并讨论该体系结构的特性和进一步研究的问题．     

A tunable reentrant resonator with transverse orientation of electric field for in vivo EPR spectroscopy

There has been a need for development of microwave resonator designs optimized to provide high sensitivity and high stability for EPR spectroscopy and imaging measurements of in vivo systems. The design and construction of a novel reentrant resonator with transversely oriented electric field (TERR) and rectangular sample opening cross section for EPR spectroscopy and imaging of in vivo biological samples, such as the whole body of mice and rats, is described. This design with its transversely oriented capacitive element enables wide and simple setting of the center frequency by trimming the dimensions of the capacitive plate over the range 100-900 MHz with unloaded Q values of approximately 1100 at 750 MHz, while the mechanical adjustment mechanism allows smooth continuous frequency tuning in the range +/-50 MHz. This orientation of the capacitive element limits the electric field based loss of resonator Q observed with large lossy samples, and it facilitates the use of capacitive coupling. Both microwave performance data and EPR measurements of aqueous samples demonstrate high sensitivity and stability of the design, which make it well suited for in vivo applications.     

压力对聚苯胺导电性的影响

 导电高聚物聚苯胺薄膜经过定向拉伸后，其有序度、电导及跃迁势垒都发生了很大变化。本文研究了准静水压力对定向拉伸前后，聚苯胺薄膜电学性质的影响。发现未定向拉伸的聚苯胺薄膜的电导随压力单调增加，跃迁势垒T₀随压力单调减少，而定向拉伸后的聚苯胺薄膜则在0.47 GPa出现电导的极大值，在0.35~0.71 GPa之间出现T₀的极小值，这个异常行为与聚乙炔、聚噻吩等导电高聚物均不相同。