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排序方式: 共有160条查询结果,搜索用时 15 毫秒
1.
G. D. Manolis P. S. Dineva T.V. Rangelov 《光散射学报》2005,17(3):289-291
pacc:0200,8100,4210h Wavediffractionininhomogeneouscracked continuawithadepth-dependentshearmodulus andunderconditionsofplanestrainisstudied herein.Arestrictedtypeofinhomogeneityiscon sidered,wherePoisson sratioisfixedatone-quarter,whilebothshearmodulusan… 相似文献
2.
Bermel W Bertini I Felli IC Matzapetakis M Pierattelli R Theil EC Turano P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,188(2):301-310
Attempts are made to efficiently decouple (13)C nuclei without significant loss of coherence during the application of the decoupling package. Such attempts are based on the S(3)E spin-state selection method. A newly developed double S(3)E (DS(3)E) is particularly efficient for C(alpha) detection for proteins as large as 480 kDa. 相似文献
3.
T. Pradell J. Molera E. Pantos A.D. Smith C.M. Martin A. Labrador 《Applied Physics A: Materials Science & Processing》2008,90(1):81-88
Luster is a golden metallic-like decoration produced on glazed ceramics since early Islamic times (Iraq, 9th AD). Luster is
obtained by the reaction of a luster paint and the glaze surface over which it is applied. A temperature-resolved XRD experiment
was designed to study the high temperature reactions in the luster paint while the luster layer is formed. The luster paint
composition has been made based on the original luster paints found during the excavation of the 13th AD workshop site at
Paterna (Valencia).
The sulfo-reducing atmosphere created during the decomposition of cinnabar promotes the reduction of Cu2+ containing compounds to Cu+ and the presence of Hg vapours delays the precipitation of metal silver. Moreover, evidence of the formation of a melt in
which the copper and silver-containing compounds dissolve has also been obtained.
The thickness of the luster paint applied results in the formation of luster layers of different hues and colours. The use
of a mixture of copper and silver paint results in the formation of dark-brown luster layer similar to the ones produced in
early Islamic times in Iraq and showed also the characteristic blue iridescences.
PACS 81.05.Pj; 81.07.-b; 78.67.-n; 82.39.Wj 相似文献
4.
Photoemission yield spectra of solid argon using synchrotron radiation for excitation in the photon energy range 11.7–16 eV show peaks closely following the known excitonic transitions, further peaks at 11.96 and 13.1 eV and also give an indication for band-gap photoconductivity. 相似文献
5.
Holmstrand H Mandalakis M Zencak Z Gustafsson O Andersson P 《Journal of chromatography. A》2006,1103(1):133-138
Chlorine isotope fractionation during preparative capillary gas chromatography (pcGC) was investigated using 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) as a model compound for semi-volatile organochlorine (OCl) molecules. Chlorine isotope analysis by thermal ionization mass spectrometry revealed no significant alteration of the chlorine isotope composition when the whole peaks were collected in pcGC (delta37Cl -3.2 per thousand versus -3.6 per thousand for the unprocessed DDT, +/-0.5 per thousand SD). However, distinct isotope fractionations were measured for the front (delta37Cl -5.1 per thousand) and tail (delta37Cl -1.8 per thousand) segments of partially collected samples. Isolation of individual OCls by pcGC enables accurate off-line chlorine isotope analysis, and thus facilitates the investigation of naturally occurring OCls. 相似文献
6.
Manolis M. Antonakis Alexandra Tsirigotaki Katerina Kanaki Constantinos J. Milios Spiros A. Pergantis 《Journal of the American Society for Mass Spectrometry》2013,24(8):1250-1259
In this study, we report on the development of a novel nebulizer configuration for sonic-spray ionization (SSI) mass spectrometry (MS), more specifically for a version of SSI that is referred to as Venturi easy ambient sonic-spray ionization (V-EASI) MS. The developed nebulizer configuration is based on a commercially available pneumatic glass nebulizer that has been used extensively for aerosol formation in atomic spectrometry. In the present study, the nebulizer was modified in order to achieve efficient V-EASI-MS operation. Upon evaluating this system, it has been demonstrated that V-EASI-MS offers some distinct advantages for the analysis of coordination compounds and redox active inorganic compounds over the predominantly used electrospray ionization (ESI) technique. Such advantages, for this type of compounds, are demonstrated here for the first time. More specifically, a series of labile heptanuclear heterometallic [CuII 6LnIII] clusters held together with artificial amino acid ligands, in addition to easily oxidized inorganic oxyanions of selenium and arsenic, were analyzed. The observed advantages pertain to V-EASI appearing to be a “milder” ionization source than ESI, not requiring electrical potentials for gas phase ion formation, thus eliminating the possibility of unwanted redox transformations, allowing for the “simultaneous” detection of negative and positive ions (bipolar analysis) without the need to change source ionization conditions, and also not requiring the use of syringes and delivery pumps. Because of such features, especially because of the absence of ionization potentials, EASI can be operated with minimal requirements for source parameter optimization. We observed that source temperature and accelerating voltage do not seem to affect labile compounds to the extent they do in ESI-MS. In addition, bipolar analysis of proteins was demonstrated here by acquiring both positive and negative ion mass spectra from the same protein solutions, without the need to independently adjust solution and source conditions in each mode. Finally, the simple and efficient operation of a dual-nebulizer configuration was demonstrated for V-EASI-MS for the first time. Figure
? 相似文献
7.
Stratakis M Kalaitzakis D Stavroulakis D Kosmas G Tsangarakis C 《Organic letters》2003,5(19):3471-3474
[reaction: see text] The ene reaction of singlet oxygen with chiral trisubstituted alkenes bearing an alkyl and a phenyl group at the stereogenic center is erythro diastereoselective in solution and threo diastereoselective if carried out within zeolite Na-Y. The change of the diastereoselection trend by zeolite confinement is attributed to a synergism of steric effects and cation-pi interactions. 相似文献
8.
9.
Kanaze FI Termentzi A Gabrieli C Niopas I Georgarakis M Kokkalou E 《Biomedical chromatography : BMC》2009,23(3):239-249
The flavonoid content of several methanolic extract fractions of Navel orange peel (flavedo and albedo of Citrus sinensis) cultivated in Crete (Greece) was first analysed phytochemically and then assessed for its antioxidant activity in vitro. The chemical structures of the constituents fractionated were originally determined by comparing their retention times and the obtained UV spectral data with the available bibliographic data and further verified by detailed LC-DAD-MS (ESI+) analysis. The main flavonoid groups found within the fractions examined were polymethoxylated flavones, O-glycosylated flavones, C-glycosylated flavones, O-glycosylated flavonols, O-glycosylated flavanones and phenolic acids along with their ester derivatives. In addition, the quantitative HPLC analysis confirmed that hesperidin is the major flavonoid glycoside found in the orange peel. Interestingly enough, its quantity at 48 mg/g of dry peel permits the commercial use of orange peel as a source for the production of hesperidin. The antioxidant activity of the orange peel methanolic extract fractions was evaluated by applying two complementary methodologies, DPPH(*) assay and the Co(II)/EDTA-induced luminol chemiluminescence approach. Overall, the results have shown that orange peel methanolic extracts possess moderate antioxidant activity as compared with the activity seen in tests where the corresponding aglycones, diosmetin and hesperetin were assessed in different ratios. 相似文献
10.
Adam W Krebs O Orfanopoulos M Stratakis M Vougioukalakis GC 《The Journal of organic chemistry》2003,68(6):2420-2425
The intramolecular and intermolecular kinetic isotope effects (KIE) have been determined for the nitrosoarene ene reaction with deuterium-stereolabeled 2,3-dimethyl-2-butenes (TME). trans-TME-d(6) (k(H)/k(D) = 3.0) and gem-TME-d(6) (k(H)/k(D) = 4.0) show large intramolecular primary isotope effects. In contrast, the intramolecular competition in cis-TME-d(6) (k(H)/k(D) = 1.5) and the intermolecular competition for the TME-d(0)/TME-d(12) pair (k(H)/k(D) = 1.98) show considerably smaller, but mechanistically significant kinetic isotope effects. The latter fact is rationalized in terms of reversible formation of a three-membered-ring intermediate, namely the aziridine N-oxide, or a similar unsymmetrical, polarized diradical in the first step of the reaction. Such reversibility has also been implied earlier for triazolinedione (TAD) and singlet oxygen ((1)O(2)) with deuterium-stereolabeled 2-butenes, but of the three enophiles, ArNO is the most sensitive toward reversibility, which is due to its moderate reactivity and its high steric demand. 相似文献