Absolute configuration of chirally deuterated neopentane

The relationship between macroscopic chirality and chirality on the molecular level was unequivocally established in 1951 through anomalous X-ray scattering. Although this technique became the definitive method for determining the absolute configuration of a molecule, one important limitation of the approach is that the molecule must contain 'heavy' atoms (for example, bromine). The direct determination of absolute configurations for a wider range of molecules has recently become possible by measuring a molecule's vibrational optical activity. Here we show that instrumental advances in Raman optical activity, combined with quantum chemical computations, make it possible to determine the absolute configuration of (R)-[2H1, 2H2, 2H3]-neopentane. This saturated hydrocarbon represents the archetype of all molecules that are chiral as a result of a dissymmetric mass distribution. It is chemically inert and cannot be derivatized to yield molecules that would reveal the absolute configuration of the parent compound. Diastereomeric interactions with other molecules, optical rotation, and electronic circular dichroism are, in contrast to the well-known case of bromochlorofluoromethane, not expected to be measurable. Vibronic effects in the vacuum ultraviolet circular dichroism might reveal that the molecule is chiral, but the presence of nine rotamers would make it extremely difficult to interpret the spectra, because the spatial arrangement of the rotamers' nuclei resembles that of enantiomers. The unequivocal spectroscopic determination of the absolute configuration of (R)-[2H1, 2H2, 2H3]-neopentane therefore presented a major challenge, one that was at the very limit of what is possible.     

提取玫瑰精油的研究

本文在比较各种提取玫瑰精油方法的基础上,提出一个简便易行,产率适中的提取方法——稀碱发酵法。     

Absolute measures of the completeness of the fossil record

Measuring the completeness of the fossil record is essential to understanding evolution over long timescales, particularly when comparing evolutionary patterns among biological groups with different preservational properties. Completeness measures have been presented for various groups based on gaps in the stratigraphic ranges of fossil taxa and on hypothetical lineages implied by estimated evolutionary trees. Here we present and compare quantitative, widely applicable absolute measures of completeness at two taxonomic levels for a broader sample of higher taxa of marine animals than has previously been available. We provide an estimate of the probability of genus preservation per stratigraphic interval, and determine the proportion of living families with some fossil record. The two completeness measures use very different data and calculations. The probability of genus preservation depends almost entirely on the Palaeozoic and Mesozoic records, whereas the proportion of living families with a fossil record is influenced largely by Cenozoic data. These measurements are nonetheless highly correlated, with outliers quite explicable, and we find that completeness is rather high for many animal groups.     

负绝对温度系统的统计讨论

本文对负绝对温度系统进行了统计讨论，导出并分析了典型的核自旋负温系统的Ｓ和ＣＢ的表达式。     

缓发中子有效份额的测量及计算方法

缓发中子有效份额βeff是反应堆重要的动态参数,研究仅基于实验数据的βeff测量方法很有意义。首先,采用多路定标器(multi channel system,MCS)时间多道卡搭建数据采集平台,在清华大学工程物理系反应堆物理实验室的次临界装置上展开微观中子噪声的实验工作,利用双区Rossi-α方法分析实验测量的结果,以数值拟合的方式得到βeff的数值;同时研究基于Monte Carlo方法的中子-光子输运程序(Monte Carlo N-particle transport code,MCNP)软件在βeff计算方面的应用,计算次临界装置的相关动态参数。实验测量结果与计算结果符合良好,确认了实验方法的有效性。     

Fuzzy实直线上级数的绝对收敛性

证明了Fuzzy实直线上的绝对收敛的级数经过重排后其和不变,     

Fourier-Legendre级数的绝对收敛

讨论尚未被研究的ＦｏｕｒｉｅｒＬｅｇｅｎｄｒｅ级数的绝对收敛问题．     

热力学中的绝对熵

一般认为热力学中只能定义熵差,只有在统计物理中才能定义绝对熵.实际上由不确定关系确定热力学系统基态,在热力学中也可以确定绝对熵.     

关于砂轮表面形貌的研究

针对砂轮表面形貌的特征,就砂轮表面形貌本身与磨削输出量之间的关系进行了具体研究,提出表征砂轮形貌的基本参数,着重分析了砂轮形貌的基本参数在磨削过程中的变化与磨削效果的关系,得出砂轮修整的方法。     

Walch-Fourier级数的绝对收敛性

针对多种情况证明了Walch-Fourier级数的绝对收敛性,拓广了文献[4]、[5]的部分结果.     

扭立方体连接网络的可重构性研究

网络的可重构技术是容错计算机技术的一个重要组成部分。首先讨论扭立方体连接网络中子图的领接关系,然后研究冗余重构技术在扭立方体连接网络上的实现问题。     

黑格尔绝对精神论域中的历史实践观

黑格尔在继承、扬弃前人思想的基础上以历史的视角展开对实践的探寻,由此第一次提出了劳动实践的概念。对生产实践的深入挖掘,使黑格尔看到了其内在的中介性与目的性、社会性与普遍性及其内蕴的经济关系,但由于其绝对精神的幽灵作怪,因而只能是一种抽象精神的道德实践。