New aspects of diphenylbutadiene photochemistry. Regiospecific hula-twist photoisomerization

In EPA glass at liquid nitrogen temperature, the E,E isomer of diphenylbutadiene (DPB) was photostable, while both the Z,E and Z,Z isomers underwent selective HT isomerization at center 1 giving the stable conformer of the double-bond isomerized trans product. That HT-1 was involved rather than the OBF process was shown by results of o,o'-dimethyl-DPB. Formation of unstable trans product corresponded to simultaneous configurational and conformational isomerization. The regioselectivity was found not sensitive to a substituent effect, as shown by the similar reactivity in p,p'- or o,o'-bistrifluoromethyl-DPB.     

Cover Picture

The cover picture shows the X-ray structure of a squalene-hopene cyclase (ribbon diagram) in the center. Squalene and 2,3-oxidosqualene cyclases catalyze the formation of up to five rings and nine stereocenters in transformations that are both complex and elegant. The triterpenes which are arranged around the structure outline the principal reaction pathways for the enzymatic conversion of oxidosqualene (upper semicircle) and squalene (lower semicircle). Further details about these fascinating reactions are discussed by Schulz, Liu et al. on p. 2812 ff.     

电磁理论中算符的一些性质

在本文中,把在不均匀各向异性介质中的麦克斯韦方程看作算符,它定义在一个有界区域,可以被理解为微波技术中的谐振腔。但在这腔中充填着铁氧体,等离子体或其他各向异性介质,这些介质在应用中日益重要。文中证明了在某些μ、ε和边界条件下,算符成为对称。而对称性和自伴性在本征函数展开中带来很多方便;此外我们推导了本征振动的正变性和互易定理。如果不满足对称性,引入伴谐振腔的概念,所谓伴谐振腔在几何形状上和原来的腔相同,但ε、μ和边界条件不一样。它和自伴谐振腔在正交性和互易定理上有某些相似之处。     

Influence of spectral resolution on absorption-line profiles

The convolution of the instrumental function with the initial line profile resulting in the observed intensity distribution has been analyzed by computer studies. Detailed information about its influence on half-width and total absorption is obtained for a wide range of characteristic parameters.     

关于波导管的格林张量函数

本文以本征函数展开的方法,研究了波导管中格林函数的一般性质和形式。为了得到波导管的本征函数(简正波)和格林张量函数的一些关系,我们首先对格林函数作富氏变换,它的象函数在各向同性介质波导中以并矢形式作为最简单的表达方法,而在充有各向异性介质波导中可以表为ABA⁺e^-ikz₀的形式,这里A是坐标矩阵。用这种方法详细推导了均匀各向同性介质波导中的并矢格林函数。 关键词：     

Electron Excited M X-Ray Spectra of the Elements 55≤Z≤58

The M emission spectra of the elements 55 Cs, 56 Ba, 57 La, and 58 Ce were measured using wavelength dispersive X-ray spectrometry with a TAP crystal as the dispersing element. In total, 34M lines were observed, of which only 13 are contained in the compilation of Bearden. M and M of 56 Ba are among the new lines. They have their origin in a similar process to one that is known for 57 La. The interpretation of these spectra is complicated by the strong overlap of some emission lines with the M_IV,V absorption structures, which may lead to anomalous self-absorption effects. Therefore, we have concentrated on spectra taken at a low energy of the exciting electrons, E₀=2.5keV. However, in order to illustrate the anomalous self-absorption effects parts of the 2.5keV spectra, of Ba and La, are shown in comparison with the 10keV spectra.     

M Spectra of the Rare Earth Elements Measured with an Ultra-Thin Window Si(Li) Detector

The oxides of the rare earth elements 57Z71 were excited by electrons with an energy between 3 and 15keV. X-rays were detected by an energy dispersive Si(Li) spectrometer, with an ultra-thin polymer entrance window. Due to the limited resolution of this type of spectrometer, the M spectra of the rare earths appear to consist of only four peaks: M, M,, M, and M₂N₄. The net height of these peaks relative to that of M, was used as a measure of the relative intensity. For 3keV electrons, a continuous decrease of the relative intensity of M with increasing Z was observed, ranging from approximately 90% for 57 La to less than 10% for 71 Lu. This behaviour is in agreement with a model involving a gradual filling up of the levels N6 and N7 with increasing Z. The relative intensity of M is lower than that of M by about a factor of 5, whereas M₂N₄ is approximately half as intense as M.     

Selective ultratrace analysis of 41Ca by laser resonance ionization

A compact resonance ionization mass spectrometer is presented. It is presently applied for sensitive and highly selective ultratrace determination of the long-lived radioisotope ⁴¹Ca for environmental, biological, and fundamental investigations. The development of coherent multistep resonance ionization enables the realization of experimental detection limits as low as10⁶ atoms per sample and very high isotopic selectivity above 10¹². This revised version was published online in August 2006 with corrections to the Cover Date.     

青藏铁路多年冻土区工程复杂性分析

青藏铁路穿越550km多年冻土区,多年冻土地温、冻土类型以及沿线生态环境等存在较大的差异,使多年冻土区工程较为复杂。因此本文提出了冻土工程复杂性概念,建立冻土工程复杂性评价模型,并利用GIS平台对青藏铁路沿线唐古拉山越岭地段工程复杂性进行了分析和研究。研究结果表明,青藏铁路穿越的唐古拉山越岭地段工程复杂性相对较小,而青藏公路的工程复杂性相对较大。这表明了青藏公路沿线冻土工程比青藏铁路沿线更为复杂,在各种因素的影响下,青藏公路路基稳定性变化比青藏铁路更加复杂。