Self-intersections of curves on surfaces

Let M be a compact orientable surface with nonempty boundary (x(M)<0) and fundamental group . Let be a geodesic on M (with a fixed hyperbolic structure), and let W be a (cyclically reduced) word in a fixed set of generators of which represents . In this paper, we give an algorithm to count the number of self-intersections of in terms of W, generalizing a result of Birman and Series, where an algorithm was given to decide if was simple. Some applications of the algorithm to surfaces with one boundary and the Markoff spectrum are also given.     

低碳烃芳构化过程中HZSM－5催化剂结炭规律的研究

用ＧＣ、ＴＰＯ－ＧＣ、ＮＨ＿３－ＴＰＤ和ＴＥＭ等方法，测定了丙烷在ＨＺＳＭ－５沸石上芳构化过程中，催化剂的活性、结炭量、结炭Ｃ／Ｈ比、酸密度等，考察了催化剂的结炭量与其它参数之间的关系。结果表明，在反应温度为８７３Ｋ，进料空速ＷＨＳＶ＝５ｈ￣（－１）时，丙烷在ＨｚＳＭ－５上的结炭首先发生在沸石晶体的外表面的活性中心上（结炭量１．８％之前）；结炭量为１．８～３．４％时，主要在孔道交叉点结炭；结炭量在３．４～５．７％时，孔道已有受限或阻塞现象发生，导致一些富氢的结炭物在孔道内生成。     

A facile approach to surface graft vinyl acetate onto polyolefin articles

A facile and environment friendly approach was developed to graft vinyl acetate (VAc) onto plastic articles in an aqueous solution using tert‐butyl alcohol (TBA) as a compatiblizer and benzoyl peroxide (BPO) as an initiator. In a novel setup, excessive monomer suspended in a water phase, VAc could be conveniently grafted on the model substrate of low‐density polyethylene (LDPE) film and the graft percentage (GP) could be developed up to 7.3%. Reaction temperature could increase GP significantly, while adding monomer over a critical volume did not influence GP. By adding some paradioxybenzene, i.e. 0.06–0.08% in VAc phase, homopolymer PVAc could be avoided practically, while graft polymerization proceeded favorably in aqueous solutions. It was proved by attenuated total reflection‐infrared (ATR‐IR) spectroscopy that grafted VAc was located mainly at the surface of the LDPE film and hydrophilic nature of both grafted and alcoholyzed films were improved via contact angle measurements. Copyright © 2004 John Wiley & Sons, Ltd.     

四足配体铽配合物-蒙脱土超分子复合发光材料的插层组装、表征和性质研究

用两种方法分别将四足配体铽配合物[TbL（NO3）]^2＋和[TbL]^3＋插层组装到了蒙脱土（MT）层板间，制备出超分子复合发光材料[TbL（NO3）^2＋-MT和[TbL]^3＋-MT。方法一：通过离子交换反应让配离子[TbL（NO3）]^2＋取代钠＋基蒙脱土（Na-MT）中的Na^＋离子，插层组装到蒙脱土层板间。方法二：用配体L与铽基蒙脱土（Tb-MT）反应，使配体插入蒙脱土层板间与Tb^3＋离子配位。用元素分析、XRD，FT-IR,UV-vis和热分析对材料进行了表征，并对其荧光性质进行了研究。结果表明，复合材料保持了蒙脱土良好的层柱结构特征，其层间距d001值与插层配离予的直径吻合较好，配离子以单层形式分布于蒙脱土层板间，复合材料中配合物的热稳定性有明显提高。在紫外光激发下，复合材料发出较强的Tb^3＋特征荧光，其发射光谱与相应配合物的发射光谱很相似；复合材料中配合物的相对荧光强度较相应纯配合物有明显提高。荧光寿命较长；配合物的激发波长向可见光区发生位移，说明插层组装实现了对配合物激发波长的调制作用。     

二(1,8萘啶氮氧化物)合硝酸钍(Ⅳ)和铀酰(Ⅱ)配合物的合成及其性质

制得二(1,8-萘啶氮氧化物)合硝酸钍和铀酰配合物,元素分析确定其组成为Th(C_3H_6N_2O)_2(NO_3)_4和UO_2(C_3H_6N_2O)_2(NO_3)_2。通过红外光谱、荧光光谱、摩尔电导、差热热重分析等方法,研究了配合物的性质。     

The application of C-N.M.R. spectroscopy to the determination of the stereochemistry of Diels-Alder adducts

Long-range (³J) ¹³C-H coupling is a reliable probe to evaluate the stereochemistry of cycloaddition products. The method is best applied to carbonyl containing adducts but not restricted to them. Several structures have been revised and new ones evaluated.     

Crystal structures of the complexes of rare earth picrates with N, N, N′, N′-tetraphenyl-3, 6-dioxaoctanediamide

The complexes of rare earth picrate with N, N, N′, N′-tetraphenyl-3, 6-dioxaoctanediamide (TDD), [Eu(pic)₃(TDD)]-2CH₃CN and [Y(pic)₃(TDD)], have been synthesized. The crystal structures reveal that TDD acts as a tetradentate ligand, forming a ring-like coordination structure with its oxygen atoms together with one oxygen atom of the bidentate picrate. In the Eu (III) complex, the europium ion with a larger ionic radius lies out of the ring, while in the Y (III) complex, the yttrium ion with a smaller ionic radius enters the cavity of the ligand. The structures of the complexes are greatly affected by the ionic radii due to participation of the picrates in coordination. Project supported by the National Natural Science Foundation of China, the Doctoral Foundation of the State Education Commission of China, and the Climb Plan Foundation of the State Science and Technology Commission of China.