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排序方式: 共有211条查询结果,搜索用时 15 毫秒
1.
Schmidt A Habeck T Merkel L Mäkinen M Vainiotalo P 《Rapid communications in mass spectrometry : RCM》2005,19(16):2211-2216
Pyrazolium-3-carboxylate and indazolium-3-carboxylate, which belong to the class of pseudo-cross-conjugated mesomeric betaines and which represent the electronically relevant partial structures of the betaine alkaloid Nigellicin, were examined by electrospray ionization mass spectrometry. These compounds decarboxylate to pyrazol-3-ylidene and indazol-3-ylidene. The formation of adducts of these new nucleophilic carbenes under the measurement conditions was examined. 相似文献
2.
Planer-Friedrich B Matschullat J Merkel BJ Roewer G Volke P 《Analytical and bioanalytical chemistry》2002,374(7-8):1191-1198
The formation of volatile organic and inorganic metals and metalloids in aquatic environments is a known, but not very intensively investigated, process. Several techniques have been developed over the past 10 years to determine these trace components. These techniques are of limited use in wetland environments, where samples have to be taken from the soil-water interface, and require an immediate sample analysis due to thermodynamic instabilities of the volatile metal(loid)s. This paper presents an innovative sampling technique for total concentrations of volatile metal(loid)s in wetlands, based on an in situ gas-water separation via a porous PTFE membrane and stabilising the volatile metal(loid)s in a liquid sorbent (NaOCl solution). Samples may thus be collected even at remote sites, where longer storage times have to be accounted for. The sampling system was tested by means of a laboratory facility simulating the generation of arsine and dimethyl arsine under abiotic conditions as well as under field conditions. Results for sampling efficiency, reproducibility, and long-term storage are presented. Application of the sampling system in the field is shown. 相似文献
3.
4.
Bockhorst M. Burbach G. Burgwinkel R. Empt J. Guse B. Guse B. Haas K. -M. Hannappel J. Heinloth K. Hey T. Hoffmann-Rothe P. Honscheid K. Jahnen T. Jakob H. P. Jöpen N. Jüngst H. Kirch U. Klein F. -J. Kostrewa D. Lindemann L. Link J. Manns J. Menze D. Merkel H. Merkel R. Neuerburg W. Paul E. Plötzke R. Schenk U. Schmidt S. Scholmann J. Schütz P. Schultz-Coulon H. -C. Schweitzer M. Schwille W. J. Tran M. -Q. Umlauf G. Vogl W. Wedemeyer R. Wehnes F. Wißkirchen J. Wolf A. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):37-47
The reactions pK
+ and pK
+ 0 have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the 0 polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and 0 is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I 相似文献
5.
6.
M. P. Merkel V. L. Dimonie M. S. El-Aasser J. W. Vanderhoff 《Journal of polymer science. Part A, Polymer chemistry》1987,25(5):1219-1233
The particle morphology and percent grafting were investigated as a function of the crosslink density of the seed latex in two systems of core/shell latexes of polybutadiene/polymethyl methacrylate (PB/PMMA) and styrene–butadiene rubber/polymethyl methacrylate (SBR/PMMA) prepared by seeded emulsion polymerization at 50°C. The thin layer chromatography/flame ionization detection (TLC/FID) technique was used to characterize the grafting efficiency of the core/shell latexes. The percent grafting of the shell polymer was found to decrease with increasing the crosslink density of the core material. The particle morphology and precent grafting were also investigated as a function of composition and structure of the core material in four core/shell latex systems: polybutadiene/styrene–acrylonitrile copolymer (PB/SAN), (styrene-butadiene) random copolymer/styrene acrylonitrile copolymer (S:B/SAN), polystyrene : polybutadiene/styrene-acrylonitrile copolymer (PS:PB/SAN) and Kraton/styrene-acrylonitrile copolymer (Kraton/SAN), which were prepared by direct emulsification for the seed followed by emulsion polymerization at 70°C for the shell polymer. Grafting and crosslinking of the core material were found to be competitive reactions depending on the microstructure of the seed latex. 相似文献
7.
Unambiguous evidence for the participation of singlet oxygen ( 1 ) in photodynamic oxidation of amino acids 总被引:11,自引:0,他引:11
Abstract— A variety of experimental tests have been applied to the methylene-blue-sensitized photooxidation of amino acids to distinguish between singlet oxygen and non-singlet oxidation mechanisms. Conventional flash photolysis and laser photolysis were used to measure the rate constants for the quenching of excited triplet sensitizer and singlet oxygen by the amino acids histidine. tryptophan and methionine and the nucleotide guanosine-5′-monophosphate. In the case of histidine, the rate constants alone rule out an oxidation mechanism involving direct reaction with excited dye. With the other amino acids, and with guanosine monophosphate, the oxidation rates might be accounted for by either mechanism. The inhibition of the photo-oxidation of both tryptophan and methionine as well as histidine by the singlet-oxygen quenchers N3? and tetramethylethylene suggests that these reactions occur via a singlet-oxygen mechanism. A newly developed test of singlet oxygen reactions involving a comparison of photooxidation rates in normal and perdeuterated solvents has been used to establish that the photooxidation of tryptophan proceeds primarily by a singlet-oxygen mechanism. These experiments appear to constitute the first proof that singlet oxygen is involved in the photooxidation of the three amino acids tryptophan, methionine and histidine. 相似文献
8.
M. Bourquin R. M. Brown Y. Chatelus J. C. Chollet A. Degré D. Froidevaux A. R. Fyfe J. -M. Gaillard C. N. P. Gee W. M. Gibson R. J. Gray P. Igo-Kemenes P. W. Jeffreys B. Merkel R. Morand R. J. Ott H. Plothow J. -P. Repellin B. J. Saunders G. Sauvage B. Schiby H. W. Siebert V. J. Smith K. -P. Streit R. Strub J. J. Thresher 《Zeitschrift fur Physik C Particles and Fields》1982,12(4):307-321
The charged hyperon beam at the CERN Super Proton Synchrotron (SPS) has been used to collect data on semileptonic decays ofΣ ?,Ξ ? andΛ. A magnetic channel selects 100 GeV/c negatively charged particles produced in the forward direction by interaction of the 200 GeV/c SPS proton beam on a BeO target. TheΣ ? andΞ ? hyperons are concurrently identified in a DISC ?erenkov counter, and their decay products are analysed by a magnetic spectrometer. Electron-hadron discrimination is achieved by the combined use of lead-glass and lead/scintillator counters, transition radiation detectors, and a ?erenkov counter. In this article we report results on the \(\Sigma ^ - \to \Lambda e^ - \bar v\) decay mode. Measurements of the Λ polarization and of the centre-of-mass distributions (baryon kinetic energy, electron-neutrino correlation, and Dalitz plot distributions) yield the vector to axialvector form factor ratiof 1/g 1=+0.034±0.080, in agreement with the value expected from the conserved vector current hypothesis (f 1/g 1=0). TheΣ ?→Λe ? v→ branching ratio measurement gives a value of (5.41±0.30)×10?5. The effects of radiative corrections are not included in these results. They are discussed in the text. Results on the otherΞ ?,Σ ?, andΛ semileptonic decays are reported in separate articles. 相似文献
9.
In this paper,we study the surface instability of a cylindrical pore in the absence of stress. This instability is called the Rayleigh-Plateau instabilty. We consider the model developed by Spencer et ... 相似文献
10.
A Collaboration M. Makek P. Achenbach C. Ayerbe Gayoso C. Barbieri J. C. Bernauer R. B?hm D. Bosnar A. Denig M. O. Distler I. Fri??i? C. Giusti H. Merkel U. Müller L. Nungesser J. Pochodzalla S. Sanches Majos B. S. Schlimme M. Schwamb Th. Walcher 《The European Physical Journal A - Hadrons and Nuclei》2016,52(9):298