A Spirocyclohexyl Nitroxide Amino Acid Spin Label for Pulsed EPR Spectroscopy Distance Measurements

Site‐directed spin labeling and EPR spectroscopy offer accurate, sensitive tools for the characterization of structure and function of macromolecules and their assemblies. A new rigid spin label, spirocyclohexyl nitroxide α‐amino acid and its N‐(9‐fluorenylmethoxycarbonyl) derivative, have been synthesized, which exhibit slow enough spin‐echo dephasing to permit accurate distance measurements by pulsed EPR spectroscopy at temperatures up to 125 K in 1:1 water/glycerol and at higher temperatures in matrices with higher glass transition temperatures. Distance measurements in the liquid nitrogen temperature range are less expensive than those that require liquid helium, which will greatly facilitate applications of pulsed EPR spectroscopy to the study of structure and conformation of peptides and proteins.     

智能流域管理的关键问题与模型技术

在总结流域问题现状及流域管理决策需求的基础上,基于仿生学原理,类比人的思维特征和决策过程,提出了包括流域信息获取、输入-输出因果关联模拟以及优化决策等步骤在内的智能流域管理模式,并对比分析了智能流域管理和传统流域管理的差异性。提出了智能流域管理的4个关键问题：管理目标的确定、基于智能因子关联与流动的模型开发与信息获取、...     

Cubanes: Starting Materials for the Chemistry of the 1990s and the New Century

The study of non-natural products has led to a broad understanding of bonding and reactivity in organic chemistry. Many times, compounds thought impossible have been realized in the course of such studies. Cubane, a landmark in the world of “impossible” compounds, has been found to have a rich chemistry, full of the unexpected. The recent renaissance of cubane chemistry, triggered by potential applications of the system to the production of high-energy fuels and the like, has led to many discoveries including the first methods for systematic substitution on strained, saturated systems and a new process for the metalation of arenes, ortho magnesiation. Reactive intermediates with exceptional bonding parameters have been uncovered and characterized including 1(9)-homocubene, the most twisted olefin; cubene, the most pyramidalized olefin; cubyl cation, once the “least likely” cation; cubylmethyl radical, a saturated radical that rearranges on the picosecond timescale; and many other extraordinary species. There is certainly good reason to believe that future work in the cubane arena will be at least as productive (probably more so), and that it will help develop a deeper understanding of chemistry.     

The Asymptotic Distribution of Singular-Values with Applications to Canonical Correlations and Correspondence Analysis

Let X_n, n = 1, 2, ... be a sequence of p × q random matrices, p ≥ q. Assume that for a fixed p × q matrix B and a sequence of constants b_n → ∞, the random matrix b_n(X_n − B) converges in distribution to Z. Let ψ(X_n) denote the q-vector of singular values of X_n. Under these assumptions, the limiting distribution of b_n (ψ(X_n) − ψ(B)) is characterized as a function of B and of the limit matrix Z. Applications to canonical correlations and to correspondence analysis are given.     

A correction method for measuring turbulence kinetic energy dissipation rate by PIV

The accuracy of turbulent kinetic energy (TKE) dissipation rate measured by PIV is studied. The critical issue for PIV-based dissipation measurements is the strong dependency on the spatial resolution, Δx, as reported by Saarenrinne and Piirto (Exp Fluids Suppl:S300–S307, 2000). When the PIV spacing is larger than the Kolmogorov scale, η, the dissipation is underestimated because the small scale fluctuations are filtered. For the case of Δx smaller than the Kolmogorov scale, the error rapidly increases due to noise. We introduce a correction method to eliminate the dominant error for the small Δx case. The correction method is validated by using a novel PIV benchmark, random Oseen vortices synthetic image test (ROST), in which quasi-turbulence is generated by randomly superposing multiple Oseen vortices. The error of the measured dissipation can be more than 1,000% of the analytical dissipation for the small Δx case, while the dissipation rate is underestimated for the large Δx case. Though the correction method does not correct the underestimate due to the low resolution, the dissipation was accurately obtained within a few percent of the true value by using the correction method for the optimal resolution of η/10 < Δx < η/2.