On the Connection Between Oriented Percolation and Contact Process

We study the contact process in ^d and a family of two-parametric oriented percolation models in ^d × ₊. It is proved that the derivative at the endpoint of the critical curve for percolation exists and its absolute value coincides with the critical rate for the corresponding contact process.     

单轴取向聚对苯二甲酸乙二酯非等温结晶动力学研究

采用等速升温DSC方法对单轴取向聚对苯二甲酸乙二酯 (PET)的结晶过程进行了研究 ,发现单轴取向PET的冷结晶峰表现为多重结晶峰 .等温DSC方法的研究结果进一步证实结晶重峰的存在 .为此 ,本文提出了一种依据非等温DSC曲线解析高聚物结晶动力学参数的新方法 .对单轴取向PET的研究结果表明 ,与其他方法相比较 ,由新方法计算出的理论曲线与实验数据能更好地吻合 .单轴取向PET的总的结晶过程由三个子结晶过程组成 .根据不同拉伸比 ,各个子过程的Avrami指数和质量分数的变化 ,对结晶机理进行了解释 .与各向同性PET样品相比 ,单轴取向PET在低温部分的结晶速率明显增快     

薄膜用聚丙烯树脂熔融态PVT行为的研究

利用PVT 10 0分析仪对 5种不同牌号的双向拉伸用聚丙烯 (BOPP)树脂的压力 体积 温度 (PVT)特性进行了测定 ,并利用Tait方程法得出BOPP熔体的热膨胀系数 (α)随温度和等温压缩系数 (β)随压力的变化关系 .研究结果表明 ,在相同条件下 ,牌号为S2 8C的BOPP熔体的热膨胀系数、等温压缩系数和结晶熔融温度分别低于其它牌号 ,因此 ,我们推断S2 8C在冷片形成过程中的体积形变较小 ,可避免由于收缩产生的模片表面缺陷 ,进而减少在后续双向拉伸过程中的破膜现象     

Synthesis, Crystal Structure and Luminescent Properties of TbCu（TeO3）2Cl

TbCu(TeO3)2Cl was obtained in high yield from high temperature solid-state reac-ion of Tb4O7,CuO,CuCl2 and TeO2 in a 1:2:2:8 molar ratio at 710 ℃ in an evacuated quartz tube. Its structure was established by single-crystal X-ray diffraction. The title compound crystal-lizes in monoclinic,space group P21/c,with a=5.409(2),b=14.994(6),c=9.183(4),β= 98.884(5)°,V=735.8(5) ?3 and Z=4. TbCu(TeO3)2Cl is isostructural with LnCu(TeO3)2X (Ln= Dy,X= Cl; Ln=Er,X=Cl,Br). Its structure features a three-dimensional (3D) network built from Tb(Ⅲ) and Cu(II) ions interconnected by tellurite and chloride anions; the chloride anion and the lone-pair electrons of the tellurium(IV) ions are oriented toward the cavities of the tunnels in the network. Solid-state luminescent spectrum of TbCu(TeO3)2Cl shows a strong emission band at 545 nm with a luminescent life time of 291 μs.     

Fabrication of self-supported patterns of aligned beta-FeOOH nanowires by a low-temperature solution reaction

Self-supported patterns of oriented alignment of beta-FeOOH nanowires are fabricated through a simple solution reaction from the complex [Fe(phen)(3)](2+) at 60 degrees C. The alignment of nanowires with a diameter of 40 nm and length of 6 mum is relatively uniform. HRTEM studies show that the growing direction of beta-FeOOH nanowires is perpendicular to the orientation plane of self-formed beta-FeOOH flake-like substrates. In the reaction and crystal growth process, the precursor [Fe(phen)(3)](2+) is undoubtedly vital to the formation of nanowire alignment. In detail, the formation of aligned nanowires is thought to be realized by controlling two competing reactions. Electrochemical and UV-visible measurements suggest that the product might have potential applications in lithium batteries and semiconductor electronics. This synthetic process is simple, mild, clean, reproducible, and free of any template; it provides a novel pathway for the low-temperature growth of nanowires and their simultaneous oriented alignment.     

Ultrafast electron diffraction: oriented molecular structures in space and time.

The technique of ultrafast electron diffraction allows direct measurement of changes which occur in the molecular structures of isolated molecules upon excitation by femtosecond laser pulses. The vectorial nature of the molecule-radiation interaction also ensures that the orientation of the transient populations created by the laser excitation is not isotropic. Here, we examine the influence on electron diffraction measurements--on the femtosecond and picosecond timescales--of this induced initial anisotropy and subsequent inertial (collision-free) molecular reorientation, accounting for the geometry and dynamics of a laser-induced reaction (dissociation). The orientations of both the residual ground-state population and the excited- or product-state populations evolve in time, with different characteristic rotational dephasing and recurrence times due to differing moments of inertia. This purely orientational evolution imposes a corresponding evolution on the electron scattering pattern, which we show may be similar to evolution due to intrinsic structural changes in the molecule, and thus potentially subject to misinterpretation. The contribution of each internuclear separation is shown to depend on its orientation in the molecular frame relative to the transition dipole for the photoexcitation; thus not only bond lengths, but also bond angles leave a characteristic imprint on the diffraction. Of particular note is the fact that the influence of anisotropy persists at all times, producing distinct differences between the asymptotic "static" diffraction image and the predictions of isotropic diffraction theory.     

Diversity‐oriented synthesis

Diversity‐oriented synthesis (DOS), which describes the synthesis of structurally diverse collections of small molecules, was developed, in part, to address combinatorial chemistry's shortfalls. In this paper, we hope to give an indication of what can be achieved using the DOS approach to library generation. We describe some of the most successful strategies utilized in DOS, with special focus on our own area of interest; DOS from simple, pluripotent starting materials. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 129–142; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20144     

Complexity of approximating the oriented diameter of chordal graphs

The oriented diameter of a bridgeless connected undirected (bcu) graph G is the smallest diameter among all the diameters of strongly connected orientations of G. We study algorithmic aspects of determining the oriented diameter of a chordal graph. We (a) construct a linear‐time approximation algorithm that, for a given chordal bcu graph G, finds a strongly connected orientation of G with diameter at most one plus twice the oriented diameter of G; (b) prove that, for every k ≥ 2 and k # 3, to decide whether a chordal (split for k = 2) bcu graph G admits an orientation of diameter k is NP‐complete; (c) show that, unless P = NP, there is neither a polynomial‐time absolute approximation algorithm nor an α‐approximation algorithm that computes the oriented diameter of a bcu chordal graph for α < . © 2004 Wiley Periodicals, Inc. J Graph Theory 45: 255–269, 2004