Short Chain Branches Distribution Characterization of Ethylene/1-Hexene Copolymers by Using TREF + 13C-NMR and TREF + SC Methods

Summary: Short chain branches distribution (SCBD) is the key factor for high density polyethylene (HDPE) pipe materials to achieve their excellent performance for long term (50 years) applications. However, the precise SCBD characterization of these HDPE materials with relatively low content of comonomer incorporation still remained as a challenge in this field. In this work, two characterization methods, namely temperature rising elution fractionation (TREF) cross step crystallization (SC) (TREF + SC) and TREF cross ¹³C-NMR (TREF + ¹³C-NMR), have been respectively used to qualitatively and quantitatively investigate the SCBD for two HDPE pipe materials (PE-1 and PE-2 with different long term performances) with small amount of 1-hexene incorporation prepared from SiO₂-supported silyl chromate catalyst system (S-2 catalyst) during UNIPOL gas phase polymerization. The comparison of SCBD between the two samples showed that: although short chain branches of PE-2 with good performance were less than those of PE-1 with bad performance, PE-2 showed less comonomer incorporation on the low crystallinity and low molecular weight (MW) fractions keeping even higher comonomer incorporation on the high crystallinity and high MW parts compared with PE-1. This difference on the SCBD for PE-1 and PE-2 was thought to be the key factor which is responsible for their great difference on environment slow crack resistance (ESCR). Moreover, TREF + SC method further reflected the intra- and inter-molecular heterogeneities of each fraction from the two HDPE samples through the lamella thickness distribution compared with TREF + ¹³C-NMR.     

Existence of infinitely many periodic solutions for ordinary p-Laplacian systems

In this paper, we study the existence and multiplicity of non-trivial periodic solutions of ordinary p-Laplacian systems by using the minimax technique in critical point theory. We also give an example to illustrate that the obtained results are new even in the case p=2.     

Na-呋喃荷移络合物弱相互作用的密度泛函理论研究

在B3LYP／6－311＋G*水平上,对Na-呋喃体系可能存在的弱相互作用复合物进行了全自由度能量梯度优化,发现了Na-呋喃体系存在两个能量极小结构A、B,其中,结构A是Na原子的3s^1电子直接和呋喃杂环体系中的所有重原子的共轭大π 体系 相互偶合,形成一个具有Cs对称性的金属有机复合物;而结构B为Na 原子的3s^1电子主要通过杂原子O和杂环上原有的五中心六电子大π体系形成一个新的平面六中心七电子大π体系,具有C2V对称 性。结果B较结构 A 稳定3.40kJ/mol。结构A中的Na-O键长为0.38nm,<COC为106.9°,由于金属Na对呋喃杂环的作用使整个分子平面变形,C1、C2、C3、C4在同一个平面内,而05则稍微翘离平面且05原子距离由C1、C2、C3、C4 组成的平面的垂直距离约为0.035nm.结构B中Na-O键长为0.26nm,＜COC为106.8°。金属Na原子和杂环中所有的原子在同一个平面内。并在MP2和B3LYP水平下,用3－311＋G＊基组精确计算了最稳定结构B的结合能为△E＝4.5-5.1kJ/mol.     

Moser-Trudinger Inequality on Compact Riemannian Manifolds of Dimension Two

ln this paper, we prove Moser-Trüdinger inequality in any two dimensional manifolds. Let (M,g_M,) be a two dimensional manifold without boundary and (g, g_N) with boundary, we shall prove the following three inequalities: u∈H¹(M), \sup\limits_{and ||u||_{H¹(M)}}=1∫_M^{e^{4\pi u²}<+∞} u∈H¹(M), \sup\limits_{∫_M u=0, and} ∫_M|∇u|²=1∫_M^{e^{4\pi u²}<+∞} u∈H¹_0(N), \sup\limits_{and ∫_M|∇u²|=1∫_M^{e^{4\pi u²}<+∞} Moreover, we shall show that there exist of extremal functions which at tain the above three inequalities.     

Distance dependence analysis of the electron transfer reactivity for the metastable FeOH2/FeOH2 system: an ab initio investigation

A novel theoretical scheme and ab initio application in discussing the electron transfer (ET) reactivity are presented in this paper, and are also calibrated in terms of the mono-hydrated iron ion system, Fe²⁺–OH₂/Fe³⁺–OH₂. The detailed geometry optimizations have been made at UMP2(full)/6-311+G^* level, and the activation geometrical configuration and the energy have been obtained at this level of theory using the activation model and the ab initio potential energy surface fitted from MP2(full)/6-311+G^* single point energies. The corresponding energy quantities (such as the activation energy, and dissociation energy) have also been obtained at different levels of theory (HF, MP2, MP3, MP4, QCISD and PUHF, PMP2 and PMP3 with the spin-projection) and a same basis set (6-311+G^*). The electron correlation calculations include the all electron correlation and the valence electron correlation. The electronic transmission coefficient is calculated using the ab initio potential energy surface slopes and the coupling matrix element determined from the two-state model and the Slater-type d-electron wave functions. The pair distribution function is calculated using two different schemes. Taking the pair distribution function and the local ET rate into account, a statistically averaged overall observed ET rate scheme and a spherically averaged local ET rate scheme are proposed. The relevant kinetic parameters are obtained in terms of these new schemes at different ab initio calculational levels. The contact distance dependence of these parameters and the applicability of the presented models and ab initio calculational method are also discussed.     

CO…CO+ 体系相互作用的密度泛函理论研究

在三种密度泛函方法(B3LYP、B3P86及B3PW91)和两种适宜基组(6-311+G*及aug-cc-PVDZ)水平上,对CO…CO+耦合体系可能存在的相互作用复合物进行了全自由度能量梯度优化,发现势能面上存在三个能量极小点,进而作了振动频率分析加以确认.其中结构A、 B为共平面型结构, C为非共面型结构. 比较了它们之间的相对稳定性,并对其进行了轨道成键分析,计算了各原子之间的键级,同时探讨了最稳定结构A的正则振动模式. 通过消除基函数引起的基组叠加误差(BSSE)和零点振动能(ZPVE)的校正,精确求算出复合物结构A、 B和C的相互作用能△E分别为252.47、 126.70和127.12 kJ/mol, 表明CO和CO+之间存在较强的相互作用.     

反相高效液相色谱法测定ε-六硝基六氮杂异伍兹烷纯度

六硝基六氮杂异伍兹烷(HNIW)是1998年才合成的一种多环笼型硝胺高能炸药,它的学名是2,4,6,8,1O-六硝基-2,4,6,8,1O,12-六氮杂四环[5.5.O.O~(5.9).O~(3.11)]十二烷,ε-HNIW的密度、爆速及爆压超过现在含能材料领域内独鳌头的王牌炸药奥克托今(HMX)5%～8%,而由圆筒实验及钽板加速实验测得的能量输出则可超过HMX14%.目前,美国已在进行HNIW的中试生产,中国及其他国家正在积极研究HNIW的生产和应用.因此,建立HNIW纯度的分析方法,对于HNIW生产工艺改进、产品质量控制及合HNIW混合炸药和推进剂的成分分析都是迫切需要的.美国的S.A.Oehrle曾采用胶束电动色谱(MECC)及高效液相色谱(HPLC)测定了混合炸药中包括HNIW在内的十多种组分的保留时间;瑞典的B.Persson等也以HPLC测出了混合炸药中三硝基氮杂环丁烷(TNAZ)和HNIW的含量;日本的儿玉保也曾提及他们合成的HNIW经HPLC测定其纯度为99%.但上述报道均不够详细,而且多限于分析含HNIW的混合炸药.作者制得了高纯度的ε-HNIW样品,并以HPLC对所得的HNIW样品进行了纯度测定,得到峰面积归一化定量法分析结果,并对结果进行了讨论.     

苏南苏北经济发展水平差距成因探析

论文从实证方面对苏南苏北间的经济发展不平差距的基本状况作出了历史考察与总结,借助计量经济模型求解出各因素对苏南苏北经济差距的贡献程度,进而总结出苏南苏北经济差距的主要影响因素,这对指导江苏省乃至全国范围内的区域经济协调发展具有一定的借鉴意义