含液晶基团的冠醚LB膜研究

合成了含有联苯介晶基团的长链冠醚,并首次制成含液晶基团的冠醚LB膜,由LB膜的荧光光谱研究发现,与其单体在CHCl_3稀溶液中的荧光光谱相比,LB膜的荧光光谱向长波方向移动,表明分子均以缔结状态存在,XRD结果表明,LB膜具有良好的有序结构,单分子膜厚2.6nm。     

弱电场驱动下高分子链在周期管道内输运的模拟研究

采用Langevin动力学方法模拟研究了弱电场驱动下高分子链在无限长周期管道中的输运过程. 管道由长度相等的α和β两部分周期排列而成, 其中高分子链与α管道间存在相互吸引作用, 而与β管道间存在纯排斥作用. 模拟结果表明, 高分子链在输运过程中存在明显的受限阶段, 其逃离受限的方式与管道宽度有关且满足不同的规律. 对于窄管道, 高分子链在输运过程中呈直线伸展构型且运动具有“蛇爬行”特征. 高分子链逃离受限过程伴随着整条链的运动, 从而导致迁移率随高分子链长呈周期变化, 而且在迁移率极值位置, 高分子链投影长度与管道半周期之间存在简单的整数倍关系. 对于宽管道, 高分子链在输运过程中出现弯折构型且运动具有“蠕虫运动”特征. 当链长比较长时, 高分子链可通过链前端部分的伸长逃离受限, 从而导致迁移率与高分子链长度无关. 模拟结果可能有助于利用周期管道对不同长度的高分子链进行分离及可控输运.     

On periodically isotonic climate change

In a view of the past two millennia, is the recent 160-year global warmth an anomaly or a continuation of past climate pattern? In this work, we present two non-parametric χ² tests based on the U-test for the isotonic change-point problem proposed in an unpublished work by G. Shen and H. Xu (henceforth abbreviated as SX (unpublished)) and apply them to the global warming data. Our tests do not require any structure assumption on the underlying the deterministic mean process {μ_t} under the periodically isotonic alternative, but accommodate a large class of the models for the random error process. Being more attractive, the two tests obviate estimation of {μ_t} and possess explicit asymptotic distributions for short-range dependence data, and have asymptotic power 1 even under the local alternative.     

A new family of symmetric linear four-step methods for the efficient integration of the Schrödinger equation and related oscillatory problems

In this article we develop a family of three explicit symmetric linear four-step methods. The new methods, with nullified phase-lag, are optimized for the efficient solution of the Schrödinger equation and related oscillatory problems. We perform an analysis of the local truncation error of the methods for the general case and for the special case of the Schrödinger equation, where we show the decrease of the maximum power of the energy in relation to the corresponding classical methods. We also perform a periodicity analysis, where we find that there is a direct relationship between the periodicity intervals of the methods and their local truncation errors. In addition we determine their periodicity regions. We finally compare the new methods to the corresponding classical ones and other known methods from the literature, where we show the high efficiency of the new methods.     

Altering the hierarchical morphology distribution of injection molded polyethylene by the introduction of crosslink network and periodical shear

High density polyethylene (HDPE) with moderate content of crosslink network (CPE) was successfully prepared through chemical method. Specimens for structural characterization have been molded by conventional injection molding (CIM) and pressure vibration injection molding (PVIM). Influence of crosslink network on hierarchical morphology distribution and mechanical properties was systematically studied. Polarized light microscopy (PLM) revealed that both CIM and PVIM PE samples have a typical “skin-core” structure and the thickness of shear layer of CIM PE and PVIM CPE samples obviously increase. Scanning electron microscopy (SEM) showed that shish-kebab structures are clearly observed in shear layer of CIM CPE sample, indicating that the crosslink network can surely improve the formation of shish-kebab structures. Moreover, we suppose that shish-kebab structures emerged in shear and core layer of PVIM CPE sample. Wideangle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) confirmed that more orientation and shish-kebab structures form even in core layer of PVIM CPE sample, which demonstrated that the hierarchical morphology was apparently altered by periodical shear and crosslink network. Finally, the mechanical properties revealed that this oriented structure increase the tensile strength from 31 MPa of CIM PE sample to 46 MPa of PVIM CPE sample. However, the tensile behavior tended to change from ductile fracture to brittle fracture.     

Spectral emissivity modeling of steel 201 during the growth of oxidation film over the temperature range from 800 to 1100 K in air

This study explores the spectral emissivity modeling of steel 201 during the growth of oxidation film over the temperature range from 800 to 1100 K at 1.5 μm. The radiance coming from the specimen is received by an InGaAs photodiode detector. The specimen temperature is obtained by averaging the two platinum–rhodium thermocouples, which are tightly welded in the front surface of specimen near the measuring area viewed by the detector. The variation of spectral emissivity with the temperature is studied at a given heating time. The variation of spectral emissivity with the heating time is evaluated at a definite temperature. The strong oscillations of spectral emissivity are observed and discussed in detail, which originate from the interference effect between the radiation stemming from the oxidization film on the specimen surface and the radiation coming from the specimen surface. The measurement uncertainties of spectral emissivity contributed only by the surface oxidization are about 3.2–14.1%. At a given heating time, the variation of spectral emissivity with the temperature abides well by a simple analytic functional form. And at a definite temperature, the variation of spectral emissivity with the heating time can also be well reproduced by fitting except for the periodical oscillations.     

甲醛在CeO2(111)表面吸附的密度泛函理论研究

采用基于第一性原理的密度泛函理论和周期平板模型, 研究了甲醛在以桥氧为端面的CeO2(111)稳定表面上的吸附行为. 通过对不同覆盖度, 不同吸附位的甲醛吸附构型、吸附能及电子态密度的分析发现, 甲醛在CeO2(111)表面存在化学吸附与物理吸附两种情况. 化学吸附结构中甲醛的碳、氧原子分别与表面的氧、铈原子发生相互作用, 形成CH2O2物种; 吸附能随着覆盖度的增加而减小. 与自由甲醛分子相比, 物理吸附的甲醛构型变化不大, 其吸附能较小. 利用CNEB(climbing nudged elastic band)方法计算了甲醛在CeO2(111)表面的初步解离反应活化能(约1.71 eV), 远高于甲醛脱附能垒, 这与甲醛在清洁CeO2(111)表面程序升温脱附实验中产物主要为甲醛的结果相一致.     

Spectra of toroidal graphs

An n-fold periodic locally finite graph in the Euclidean n-space may be considered the parent of an infinite class of n-dimensional toroidal finite graphs. An elementary method is developed that allows the characteristic polynomials of these graphs to be factored, in a uniform manner, into smaller polynomials, all of the same size.Applied to the hexagonal tessellation of the plane (the graphite sheet), this method enables the spectra and corresponding orthonormal eigenvector systems for all toroidal fullerenes and (3, 6)-cages to be explicitly calculated. In particular, a conjecture of P.W. Fowler on the spectra of (3, 6)-cages is proved.     

Unit cell debonding analyses for arbitrary orientation of plastic anisotropy

Debonding of rigid inclusions embedded in the elastic–plastic aluminum alloy Al 2090-T3 is analyzed numerically using a unit cell model taking full account of finite strains. The cell is subjected to overall biaxial plane strain tension and periodical boundary conditions are applied to represent arbitrary orientations of plastic anisotropy. Plastic anisotropy is considered using two phenomenological anisotropic yield criteria, namely Hill [Proceedings of the Royal Society of London A 193 (1948) 281] and Barlat et al. [International Journal of Plasticity 7 (1991) 693]. For this material plastic anisotropy delays debonding compared to plastic isotropy except for the case of Hill’s yield function when the tensile directions coincided with the principal axes of anisotropy. For some inclinations of the principal axes of anisotropy relative to the tensile directions, the stress strain responses are identical but the deformation modes are mirror images of each other.     

大面积多周期伪随机序列扩散体群的一种优化布置方案

伪随机序列扩散体具有良好的扩散效果，但是大面积周期布置时会在扩散方向产生大量旁瓣。为了消除这些旁瓣，并得到符合使用者要求的扩散声压响应曲线，本文提出一种实现伪随机序列扩散体群大面积最佳布置方案的布置方法。