Submillimeter wave generation by second harmonic operation of tunable gyrotrons

The gyrotrons developed at the University of Sydney are tunable sources of millimetre and submillimetre radiation. The generation of submillimetre wavelengths requires operation at the second harmonic of the electron cyclotron frequency, or higher. Our latest gyrotron, GYROTRON IVA, has successfully achieved second harmonic operation and obtained frequencies up to 590 GHz (=0.51 mm). The experimental results and conditions for second harmonic operation will be presented. The design of a new gyrotron, GYROTRON V, which is especially optimised for the second harmonic, will also be included.     

The equator map and the negative exponential functional

We define a negative exponential harmonic map from the ballB ⁿ of ℝ_n into the sphereS ⁿ of ℝ ⁿ⁺¹ . We prove that the equator map is a negative exponential harmonic map, but not stable for the negative exponential functional whenn≥2. Moreover, we consider maps from a ballB ⁿ into the unit sphereS ^m of ℝ_m+1 wherem≥2, and prove that no nonconstant, non surjective map can reach either the minimum or the maximum of the negative exponential functional.     

空间展布体系中由化学反应-扩散-热传导耦合导致的温度场对称破缺

分析了由于化学反应-扩散-热传导耦合而导致的非等温非均匀体系中温度场对称破缺.研究结果表明,在一定的边界条件下,甚至是单组分化学反应-扩散-热传导体系,温度场的这种自组织进程也不可避免.作为温度场结构的一个范例,进一步从解析解及计算机模拟两个方面研究了小展布非等温的Lindeman模型;结果表明,温度场出现时空自组织的阈值不仅与本征参数有关,而且与体系的边界条件及外控约束相关,揭示出了诱发或避免这种温度场时空自组织之途径.     

手性Salen金属配合物与咪唑类客体分子识别的研究

用光谱滴定法研究了手性Salen金属配合物(SalenFe~(III), SalenCo~(II))与 四种咪唑类客体在CH_2Cl_2中的分子识别行为，发现手性Salen金属配合物与咪唑 ，N－甲基咪唑，2－甲基咪唑的配位数为2，与克霉唑的配位数为1。各识别体系缔 合常数的顺序对SalenFe~(III)为: K(Im) > K(2-MeIm) > K(N-MeIm) > K(GMZ)， 对SalenCo~(II)为：K(Im) > K(2-MeIm) > K(N-MeIm)。测定的识别反应的△ _rG_m~0, △_rH_m~0, △_rS_m~0表明此类识别反应为放热、熵减少的过程，反应 体系存在焓－熵补偿关系。采用分子力学和量子化学方法进行的理论研究对实验结 果作出了合理的解释。     

A note on approximate controllability for semilinear one-dimensional heat equation

The one-dimensional semilinear heat equation is considered. It is shown that if the nonlinear functionF(y) is uniformly bounded then the system is approximately controllable for every given terminal timeT>0 under some ordinary condition onb. The results may be extended to the general one-dimensional semilinear heat equation with one-dimensional control or to a boundary control heat system with semilinear boundary condition.     

Production of hybrid 16-membered macrolides by expressing combinations of polyketide synthase genes in engineered Streptomyces fradiae hosts

Combinations of the five polyketide synthase (PKS) genes for biosynthesis of tylosin in Streptomyces fradiae (tylG), spiramycin in Streptomyces ambofaciens (srmG), or chalcomycin in Streptomyces bikiniensis (chmG) were expressed in engineered hosts derived from a tylosin-producing strain of S. fradiae. Surprisingly efficient synthesis of compounds predicted from the expressed hybrid PKS was obtained. The post-PKS tailoring enzymes of tylosin biosynthesis acted efficiently on the hybrid intermediates with the exception of TylH-catalyzed hydroxylation of the methyl group at C14, which was efficient if C4 bore a methyl group, but inefficient if a methoxyl was present. Moreover, for some compounds, oxidation of the C6 ethyl side chain to an unprecedented carboxylic acid was observed. By also expressing chmH, a homolog of tylH from the chalcomycin gene cluster, efficient hydroxylation of the 14-methyl group was restored.