In vivo and in vitro investigations into the biosynthetic relatedness of the pseudopterosins

[formula: see text] Both in vivo and in vitro techniques have been developed to test putative intermediates in the biosynthetic pathway to the pseudopterosins, antiinflammatory compounds isolated from Pseudopterogorgia elisabethae. Furthermore, specific activity data we have obtained indicate that pseudopterosin A is a precursor to pseudopterosins B, C, and D. We conclude that in the biosynthesis xylose is attached to the diterpene skeleton to produce pseudopterosin A and is then aceylated to form pseudopterosins B-D.     

A Basis for the Top Homology of a Generalized Partition Lattice

For a fixed positive integer k, consider the collection of all affine hyperplanes in n-space given by xi – xj = m, where i, j [n], i j, and m {0, 1,..., k}. Let Ln,k be the set of all nonempty affine subspaces (including the empty space) which can be obtained by intersecting some subset of these affine hyperplanes. Now give Ln,k a lattice structure by ordering its elements by reverse inclusion. The symmetric group Gn acts naturally on Ln,k by permuting the coordinates of the space, and this action extends to an action on the top homology of Ln,k. It is easy to show by computing the character of this action that the top homology is isomorphic as an Gn-module to a direct sum of copies of the regular representation, CGn. In this paper, we construct an explicit basis for the top homology of Ln,k, where the basis elements are indexed by all labelled, rooted, (k + 1)-ary trees on n-vertices in which the root has no 0-child. This construction gives an explicit Gn-equivariant isomorphism between the top homology of Ln,k and a direct sum of copies of CGn.     

六顶角带谱参数杨-Baxter方程的解

通过五个解交换,四组非退化基本解和七组退化解,给出了精确可解统计模型理论中六顶角带谱参数杨-Baxter方程的全部解.并讨论了解的幺正条件. 关键词：     

包钴型γ-Fe2O3磁粉矫顽力的研究

包钴型γ-Fe₂O₃磁粉分为包钴γ-Fe₂O₃(简记为Co-γ-Fe₂O₃)和包钴包亚铁γ-Fe₂O₃(简记为CoFe-γ-Fe₂O₃)两种,它们的矫顽力可比γ-Fe₂O₃磁粉的提高100至400Oe左右,本工作对这两种磁粉矫顽力增大的原因作了探讨,认为它们矫顽力增大的机制不同:CO-γ-Fe₂O₃矫顽力增大是由于表面包覆一层Co(OH)₂使表面各向异性增大,而CoFe-γ-Fe₂O₃则是由于表面包覆的是钴铁氧体,γ-Fe₂O₃与钴铁氧体之间发生耦合作用,使矫顽力增大。     

Relative rate measurements of some reactions of hydroxyl radicals with alkanes studied under atmospheric conditions

A flow system has been developed to study relative rate coefficients of hydroxyl radicals reacting with alkanes under conditions relating to tropospheric chemistry. Relative Arrhenius parameters have been measured over the temperature range 243–328 K for pairs of alkanes from a list consisting of n-butane, 2-methylpropane, n-pentane, n-hexane, 2,2- and 2,3-dimethylbutane, 2,3,3-trimethylbutane, and 2,3,4-trimethylpentane. The results have been incorporated into a Structure-Activity Relation for hydroxylalkane reactions which leads to the following group rate coefficients for a temperature range of 240–500 K.      

Very long chains of annihilator ideals

Here we examine one of the two right Goldie conditions: the ascending chain condition on right annihilator ideals, r. ACC^⊥. One might well ask if a ring has r. ACC^⊥, does there exist a bound on the lengths of chains of right annihilator ideals? Under certain additional hypotheses, this bound does exist. In general, however, a bound does not exist, as is shown by the two example presented here.     

The kinetics of the addition of alkyl radicals to carbonyl groups. II. The addition of methyl radicals to trifluoroacetone in the gas phase. The formation reaction of the trifluoro-t-butoxy radical

By photolyzing azomethane over the temperature range 331–491 K in the presence of trifluoroacetone the kinetics of the addition reaction (1), ?H₃ + CF₃COCH₃ → CF₃C(?)(CH₃)₂ have been studied. Detailed analyses have shown that the principal product of the adduct radical, CF₃C(?)(CH₃)₂, is CH₃COCH₃ from reaction (?2), CF₃C(?)(CH₃)₂ → CH₃COCH₃ + ?F₃. The rate constant of the addition reaction has been determined to be k₁(dm³/mol s) = (4.5 ± 1.4) × 10⁷ exp(-(3370 ± 120)/T) over the temperature range 331–491 K, based on the value k₃ = 2.2 × 10¹⁰ dm³/mol s for the reaction (3), 2?H₃ → C₂H₆. The results are discussed in relation to existing data for radical additions to groups.     

电磁迴旋不稳定性的准线性理论

在有弱相对论性电子时,在电子迴旋频率Ω_e附近存在快x模的不稳定性。从这一事实出发,我们用准线性理论分析了具有粒子数倒转的分布函数引起的不稳定性最后达到饱和的物理机制。进行了一些近似的计算,求出了电磁迴旋不稳定性的饱和时间和饱和能量及垂直、平行分布函数随时间的演化过程。发现用此理论算出的饱和能级与观察到的AKR结果是一致的。 关键词：     

铝在疲劳载荷作用下所发生的基本过程

【摘　要】进行了99.6％工业纯铝和99.99％高纯铝(退火和冷加工)的扭转疲劳试验,测定了经过各种应力循环数N以后的滞后迴线的形状和面积,从而算出了在每次循环中的能量消耗ΔE和最大抗扭矩T_m。对于所得到的ΔE-N曲线和T_m-N曲线进行了分析,并与在疲劳试验的各个阶段对于试样表面所作的金相观测结果作了比较,认为在试样中未出现局部滑移区以前,引起ΔE和T_m的基本过程是空位对于位错的钉紥作用,这是一种体积效应,但是在局部滑移区出现以后,这种滑移区引起额外的能量消耗,而对于T_m的影响并不显著,因而在这个阶段里T_m和ΔE的变化便不再彼此相对应。这种分析可以澄清过去文献中关于ΔE和T_m(代表硬度变化)在疲劳过程中的变化的许多互不一致的结果。假定实验所观测到的曲线是这两种过程(整体过程和局部过程)所引起的效应的迭加,并且假定这两种过程对于ΔE和T_m的贡献由于疲劳振幅的大小、试样的处理状态(退火或冷加工)以及所合杂质之不同而异,可以满意地解释实验所观测到的各种曲线的形状和位置。这个观点的正确与否还有待于进一步的实验证实。