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81.
Colloid and Polymer Science - 20 verschieden stark vernetzte Vulkanisate eines statistischen Butadien-Acrylnitril (18)-Kopolymeren wurden in mehreren Lösungsmitteln gequollen. Dann dehnten wir... 相似文献
82.
Five routes to stable chlorins bearing 0 or 1 meso substituents have been investigated, among which reaction of a 9-bromo-1-formyldipyrromethane and 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin proved most effective. Application of this route afforded metallochlorins [Cu(II), Zn(II), and Pd(II)] including the chlorin lacking any β-pyrrole and meso substituents. 相似文献
83.
Roald Hoffmann 《Angewandte Chemie (International ed. in English)》1987,26(9):846-878
To make sense of the marvelous electronic properties of the solid state, chemists must learn the language of solid-state physics, of band structures. An attempt is made here to demystify that language, drawing explicit parallels to well-known concepts in theoretical chemistry To the joint search of physicists and chemists for understanding of the bonding in extended systems, the chemist brings a great deal of intuition and some simple but powerful notions. Most important among these is the idea of a bond, and the use of frontier-orbital arguments. How to find localized bonds among all those maximally delocalized bands? Interpretative constructs, such as the density of states, the decomposition of these densities, and crystal orbital overlap populations, allow a recovery of bonds, a finding of the frontier orbitals that control structure and reactivity in extended systems as well as discrete molecules. 相似文献
84.
Solid-state 2H NMR spectroscopy is a well-established and versatile method to study molecular orientation and dynamics in selectively deuterated samples. Herein, we introduce a 2D 2H double-quantum (DQ) NMR experiment performed under fast magic-angle spinning with a slight offset of the magic angle (OMAS). The experiment combines 2H chemical-shift resolution with DQ-filtered quasistatic 2H line shapes. In this way, it is possible to separate 2H resonances and to independently determine 2H quadrupole couplings at multiple sites. While 2H chemical shifts are resolved in the 2H DQ dimension, the quadrupole parameters can be obtained from characteristic line shapes which are reintroduced in the second dimension by the magic-angle offset. The 2D 2H DQ OMAS experiment is demonstrated on L-histidine which was deuterated at multiple sites by recrystallisation from D2O. 相似文献
85.
A method for separation and chemical identification of products formed in nuclear reactions or nuclear decay is to slow down the recoil products in a gas and to transport them to a trap, where a detecting system is arranged. The sources for the recoil products are252Cf and224Ra. As transport phase we used nitrogen or argon and added chemical reagents such as methyl and ethyl radicals, chlorine, oxygen, carbon monoxide or methane. The chemical additives lead to selective and fast separation of certain elements. As examples the results of two experiments are presented:224Ra with ethyl radicals, and252Cf with chlorine-oxygen-nitrogen mixtures. The registration of the recoil products at the trap was measured as a function of temperature, pressure and composition of the reactive gas. 相似文献
86.
N. Pilz P. Hoffmann K. H. Lieser W. Dams K. H. Nelges 《Fresenius' Journal of Analytical Chemistry》1989,335(7):695-697
Summary A non-destructive method and an experimental set-up are described by which the Pu content in UO2/PuO2 mixed oxide (MOX) pellets and in fuel rods, respectively, can be determined. The K-lines of Pu are excited by external -radiation (192Ir) and measured by a high-purity Ge detector. A calibration curve is presented and the detection limits are plotted as function of the time of measuring.
Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday 相似文献
Zerstörungsfreie bestimmung von plutonium in kernbrennstoff-stäben und -pellets
Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday 相似文献
87.
Bishop KJ Fiałkowski M Grzybowski BA 《Journal of the American Chemical Society》2005,127(45):15943-15948
Arrays of chemical oscillators are micropatterned by Wet Stamping. The technique is used to demonstrate that chemical waves can be initiated and controlled in oscillatory systems and that such waves can give rise to phenomena not observed in excitable media. Interoscillator coupling and synchronization, kinetic autofocusing, and twist-symmetry breaking are a consequence of the dependence of the oscillation phase on the local concentrations of reagents and on systems' geometry. Conditions under which a generic oscillatory system would exhibit such behaviors are determined. 相似文献
88.
W. A. Schönfeldt P. H. Mokler D. H. H. Hoffmann A. Warczak 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,4(2):161-176
For 3.6 MeV/u Sm q+ projectiles a hump in the projectile (L l +L α) x-ray emission cross section is seen as a function of charge stateq for highq with 46≦q≦52 (closed incomingL shell). This hump is attributed to the Resonant electron Transfer from the Xe target atom with simultaneous Excitation of anL 3-shell electron to theM shell. The cross section for thisL 3-shell RTE process has values up to 2·10?19 cm2, which is seen in single spectra already. To verify the existence of theL-shell RTE process for the studied collision system, extensive calculations have been carried out. Especially theL 3-shell fluorescence yield for the radiative stabilization process in the highly-charged projectile has been considered. Our calculatedq-dependent cross sections for the RTE process support the given interpretation. 相似文献
89.
1,3-Dimethylated hydrocarbon segments occur frequently as structural elements in polyketide natural products. The (13)C NMR chemical shifts of a series of model compounds containing such segments can be well reproduced by a combination of molecular mechanics and SOS-DFPT/IGLO calculations. (13)C NMR chemical shifts are calculated on MM3 geometries and are Boltzmann weighted according to the MM3 energies. On the basis of the resulting thermally averaged chemical shifts, all diastereomers of the model compounds can be unequivocally distinguished. Significant differences in chemical shifts occur at methyl groups and methylene groups that are adjacent to a single stereogenic center. The method is applied to predict the relative configuration of two stereocenters in the side chains of two natural products, sambutoxin and the bradykinin inhibitor L-755,897. 相似文献
90.
Efforts are described to design simple, fully flexible but conformationally preorganised omega-hydroxy-nonanoic acids that could serve as the conformation controlling unit in analogues of the potent protein-kinase C activator aplysiatoxin. Such analogues are macrodilactones incorporating the designed omega-hydroxy-nonanoic acid and 3,4-dihydroxy-pentanoic acid, which contains the pharmacophoric groups. The design process (replacement of CH(2) groups by an oxygen atom, annelation of a six-membered ring and placement of alkyl substituents) of the omega-hydroxy-nonanoic acids was monitored by force-field calculations. In the end of this process simple analogues of aplysiatoxin are proposed in which the proper disposition of the pharmacophoric groups is secured by a conformationally flexible but preorganised template structure as part of the macrodilactone ring. 相似文献