非自治动力系统的原像熵

本文对紧致度量空间上的连续自映射序列应用生成集和分离集引入了点原像熵、原像分枝熵以及原像关系熵等几类原像熵的定义并进行了研究.主要结果是:(1) 证明了这些熵都是等度拓扑共轭不变量.(2)讨论了这些原像熵之间及它们与拓扑熵之间的关系,得到了联系这些熵的不等式.(3)证明了对正向可扩的连续自映射序列而言, 两类点原像熵相等,原像分枝熵与原像关系熵也相等.(4)证明了对(a).由闭Riemann 流形上的一个扩张映射经充分小的C1-扰动生成的自映射序列,以及(b).有限图上等度连续的自映射序列,有零原像分枝熵.     

原子发射光谱内标法测量误差的研究

证明了原子发射光谱内标法的测量误差。当分析线和内标线的相对强度等于1时，测量误差最小。     

天然高分子表面活性剂

综述了淀粉、纤维素和壳聚糖类表面活性剂的合成方法、性质及功能。     

Kinetics of decomposition pathways of an energetic GZT molecule

This investigation uses the Gaussian 98 program, density functional theory (DFT) B3LYP/6‐31G(d,p), and ab initio MP2/6‐31G(d,p) and HF/6‐31G(d) methods to model energetic diguanidinium 5,5′‐azotetrazolate (GZT) ionic species in order to determine their decomposition mechanisms. GZT was initially cracked into two guanidinium cations (G⁺) and a 5,5′‐azotetrazolate anion (ZT^2?). Three routes—the elimination of a hydronium ion (H⁺), the elimination of a hydrogen radical (H·), and the elimination of an amine radical (·NH₂)—are suggested for the decomposition of the G⁺ cation, and three routes—single ring opening, double ring opening and N? N bond cleavage outside the ring—are proposed for the further decomposition of the ZT^2? anion. Fourteen decomposition species were obtained on splitting both the cation and anion. This result reveals the reliability of the aforementioned decomposition mechanisms. The transition state species were also obtained using a two‐structure or three‐structure synchronous transit‐guided quasi‐Newton (STQN) between the Cartesian coordinates of related particles at specific decomposition stages in this research. The corresponding activation energies in all decomposition stages were considered to infer the most feasible pathways of GZT decomposition. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Cordierite gels from TEOS and aluminum and magnesium nitrates under basic conditions

Synthesis of cordierite gels was performed using Si(OC₂H₅)₄ and aluminum and magnesium nitrates as starting materials under basic conditions. Further heat treatment yields the successive crystallisation of μ and α-cordierites and of some amounts of spinel as a secondary phase as revealed by X-ray diffraction. The poor final densification (84% of the theoretical value) of samples obtained from the as-prepared powders has been improved by ball-milling to values up to 95–98% of the theoretical value, the spinel proportion being simultaneously decreased.     

Stereoselective synthesis of new modified conformationally constrained l-tyrosine analogue with potential applications to SH2 domain ligands

This paper reports the stereoselective synthesis of a modified tricyclic tyrosine analogue 3, whose conformation is constrained by the covalent bonds and designed on the basis of X-ray and solution structures of SH2 domain and its natural peptide ligand. A Michael addition followed by an alkylation in high stereoselections, a Friedel-Crafts and a Mannich reaction-based cyclization served as the key steps in the synthesis.     

Anomalous postcritical refraction behavior for certain transversely isotropic media

Snell's law at the boundary between two transversely isotropic media with a vertical axis of symmetry (VTI media) can be solved by setting up a fourth order polynomial for the sine of the reflection/transmission angles. This approach reveals the possible presence of an anomalous postcritical angle for certain transversely isotropic media. There are thus possibly three incident angle regimes for the reflection/refraction of longitudinal or transverse waves incident upon a VTI medium: precritical, postcritical/preanomalous, and postanomalous. The anomalous angle occurs for certain strongly anisotropic media where the required root to the phase velocity equation must be switched in order to obey Snell's law. The reflection/transmission coefficients, polarization directions, and the phase velocity are all affected by both the anisotropy and the incident angle. The incident critical angles are also effected by the anisotropy.     

Synthesis of new chiral amines with a cyclic 1,2-diacetal skeleton derived from (2R, 3R)-(+)-tartaric acid

The syntheses of new chiral cyclic 1,2-diacetals from (2R, 3R)-( )-tartaric acid are described. C(2)-symmetrical diamines were prepared via direct amidation of the tartrate or from the corresponding bismesylate via reaction with sodium azide. For C1-symmetrical compounds, the Appel reaction was used to form the key intermediate, a monochlorocarbinol, from the diol. Some of the new chiral compounds, produced in good to high yields, may be potentially useful as asymmetric organocatalysts or as nitrogen and sulfur chelating ligands for asymmetric metal catalyzed reactions. Thus, a bis-N-methyl-methanamine derivative, used in substoichiometric amounts, was found to catalyze the enantioselective addition of cyclohexanone to (E)-beta-nitrostyrene with high diastereoselectivity (syn / anti = 92:8), albeit giving moderate optical purity (syn: 30 %).