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991.
Received: 11 March 1998/Revised version: 1 April 1998 相似文献
992.
Received: 21 February 1997/Revised version: 13 May 1997 相似文献
993.
Pseudopotential ab initio calculations of several gold carbides, gold nitrides and their third-row analogues have been performed
with the goal of finding species which contain triple bonds with gold. Multiple-bond character has been observed for Cl2AuCH and Cl2AuN. Bonding in these and related compounds is analysed and the reasons why gold prefers single bonds are outlined.
Received: 8 September 1997 / Accepted: 11 December 1997 相似文献
994.
C. He 《Numerische Mathematik》1997,76(4):463-477
Summary. According to the methodology of [6], many measures of distance arising in problems in numerical linear algebra and control
can be bounded by a factor times the reciprocal of an appropriate condition number, where the distance is thought of as the
distance between a given problem to the nearest ill-posed problem. In this paper, four major problems in numerical linear
algebra and control are further considered: the computation of system Hessenberg form, the solution of the algebraic Riccati
equation, the pole assignment problem and the matrix exponential. The distances considered here are the distance to uncontrollability
and the distance to instability.
Received November 4, 1995 / Revised version received March 4, 1996 相似文献
995.
996.
The introduction of UV-Vis absorption spectrophotometry to the study of radiation chemistry of polymers has opened the possibility to investigate even very opaque samples. The virgin powder polypropylene, as obtained from the industrial production line, shows after irradiation unstable products of radiolysis. Until now they were investigated mainly by EPR method. Optical absorption spectra (by diffuse reflection spectrophotometry) contribute to better identification and study of changes in time, temperature and diffusion of reactive gases. Studying the formation of stable compounds, which do not produce EPR signal, we are able to examine these species on the basis of their electronic spectra. The most important results concern the peroxides in irradiated polypropylene. 相似文献
997.
D. Praschak T. Bahners E. Schollmeyer 《Applied Physics A: Materials Science & Processing》1998,66(1):69-75
Received: 11 August 1997/Accepted: 14 August 1997 相似文献
998.
Background: The translation or stability of the mRNAs from ferritin, m-aconitase, erythroid aminoevulinate synthase and the transferrin receptor is controlled by the binding of two iron regulatory proteins to a family of hairpin-forming RNA sequences called iron-responsive elements (IREs). The determination of higher-solution nuclear magnetic resonance (NMR) structures of IRE variants suggests an unusual hexaloop structure, leading to an intra-loop G-C base pair and a highly exposed loop guanine, and a special internal loop/bulge in the ferritin IRE involving a shift in base pairing not predicted with standard algorithms.Results: Cleavage of synthetic 55- and 30-mer RNA oligonucleotides corresponding to the ferritin IRE with complexes based on oxoruthenium(IV) shows enhanced reactivity at a hexaloop guanine and at a guanine adjacent to the internal loop/bulge with strong protection at a guanine in the internal loop/bulge. These results are consistent with the recent NMR structures. The synthetic 55-mer RNA binds the iron-regulatory protein from rabbit reticulocyte lysates. The DNA analogs of the 55- and 30-mers do not show the same reactivity pattern.Conclusions: The chemical reactivity of the guanines in the ferritin IRE towards oxoruthenium(IV) supports the published NMR structures and the known oxidation chemistry of the metal complexes, The results constitute progress towards developing stand-alone chemical nucleases that reveal significant structural properties and provide results that can ultimately be used to constrain molecular modeling. 相似文献
999.
本文首先给出了最小方差集的运算模型,在此基础上指出了非负解的重要意义,并给出了非负解的枚举算法,最后给出了一个实例 相似文献
1000.
Received: 15 January 1998/Final version: 15 June 1998 相似文献