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排序方式: 共有311条查询结果,搜索用时 15 毫秒
81.
We report on the high-efficiency surface-induced dissociation of benzene and cyclohexane polyatomic ions after scattering from a rhenium oxide surface with a kinetic energy of 5–290 eV. Rhenium oxide was prepared by directly heating a rhenium metal foil, under 10?5 mbar partial oxygen pressure, at about 1000 K. Rhenium oxide is characterized by a very high work function of 6.4 eV and thus minimizes ion reneutralization probabilities. The catalytic combustion of surface organic impurities with oxygen ensures good long-term stability. We found that the surface-induced dissociation ion current is 70 times larger on rhenium oxide than on bare rhenium or stainless steel. Absolute scattered ion yields of about 50% were measured. The implications of surface-induced dissociation on mass spectrometry in supersonic molecular beams are mentioned. 相似文献
82.
T. Åkesson M.G. Albrow S. Almehed O. Benary H. Bøggild O. Botner H. Brody V. Burkert D. Cockerill S. Dagan E. Dahl-Jensen I. Dahl-Jensen P. Dam G. Damgaard G. von Dardel W.M. Evans C.W. Fabjan C. Woody 《Nuclear Physics B》1984,246(3):408-430
We study the production of identified charged particles in pp collisions at a c.m. energy of 63 GeV in events with an identified high-pT trigger particle. The measurements were performed at the CERN Intersecting Storage Rings using the Axial Field Spectrometer.Production ratios are presented as a function of pT in the range 2.5 to 8 GeV/c. 相似文献
83.
High-resolution X-ray photoelectron spectroscopy was used to demonstrate that reduction of aqueous U6+ at ferrous mica surfaces at 25 degrees C preserves U5+ as the dominant sorbed species over a broad range of solution compositions. Polymerization of sorbed U5+ with sorbed U6+ and U4+ is identified as a possible mechanism for how mineral surfaces circumvent the rapid disproportionation of aqueous U5+. The general nature of this mechanism suggests that U5+ could play an important, but previously unidentified, role in the low-temperature chemistry of uranium in reducing, heterogeneous aqueous systems. 相似文献
84.
Bassil BS Kortz U Tigan AS Clemente-Juan JM Keita B de Oliveira P Nadjo L 《Inorganic chemistry》2005,44(25):9360-9368
The 6-cobalt-substituted [{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2]22- has been characterized by IR and UV-vis spectroscopy, elemental analysis, magnetic studies, electrochemistry, and gel filtration chromatography. A single-crystal X-ray analysis was carried out on K10Na12[{Co3(B-beta-SiW9O33(OH))(B-beta-SiW8O29(OH)2)}2].49H2O (KNa-1), which crystallizes in the monoclinic system, space group P2(1)/n, with a=19.9466(8) A, b=24.6607(10) A, c=34.0978(13) A, beta=102.175(1) degrees, and Z=2. Polyanion 1 represents a novel class of asymmetric sandwich-type polyanions. It contains three cobalt ions, which are encapsulated between an unprecedented (B-beta-SiW9O34) fragment and a (B-beta-SiW8O31) unit. Polyanion 1 is composed of two sandwich species via two Co-O-W bridges in the solid state and almost certainly in solution as well based on gel filtration chromatography. UV-visible spectroscopy and cyclic voltammetry also confirmed its stability. Two well-separated groups of waves appeared in the voltammetric pattern: the wave observed in the negative potential range versus a saturated calomel electrode features the redox processes of WVI centers; the two reversible redox couples observed in the positive potential domain are attributed to the redox processes of Co2+ centers and indicated that the two types of Co2+ centers in the structure are oxidized in separate waves. Such reversibility of Co2+ centers within multi-Co-substituted polyoxometalates is uncommon. The magnetic properties of KNa-1 are also discussed. The ferromagnetic ground state has been studied by magnetic susceptibility and magnetization measurements and fitted according to an anisotropic exchange model. 相似文献
85.
Dagan Y Barr MC Fisher WM Beck R Dhakal T Biswas A Greene RL 《Physical review letters》2005,94(5):057005
The temperature, doping, and field dependences of the magnetoresistance (MR) in Pr2-xCexCuO4-delta films are reported. We distinguish between orbital MR, found when the magnetic field is applied perpendicular to the ab planes, and the nearly isotropic spin MR. The latter, the major MR effect in the superconducting samples, appears in the region of the doping-temperature phase diagram where drho/dT<0, or an upturn in the resistivity appears. We conclude that the upturn originates from spin scattering processes. 相似文献
86.
Nicolae Hurduc Cristina Damian Anca Tarus Violeta Toader Natalia Hurduc 《Central European Journal of Chemistry》2005,3(1):53-62
The main objective of this paper is to study the thermal stability of some aromatic copolyethers containing a propylenic spacer.
Some of the investigated copolyethers displayed a liquid crystalline (LC) behavior, with the presence of the mesogenic groups
in the main chain, inducing high values of the thermal transition temperatures. As a consequence, a thermal stability study
was necessary to establish the maximum temperature value for the LC behavior characterization. A thermal degradation mechanism
is proposed, taking into consideration the azobenzenic unit as the weakest link in the polymer chain and thus, the starting
point of the thermal degradation process. The degradation mechanisms were correlated with the chemical structure and the polarity
and conformation of the chains. Conformational analysis was performed using molecular simulations. Freeman-Caroll and Coats-Redfern
methods were used to calculate some kinetic characteristics. 相似文献
87.
Marks RS Margalit A Bychenko A Bassis E Porat N Dagan R 《Applied biochemistry and biotechnology》2000,89(2-3):117-126
A chemiluminescent-based optical fiber immunosensor was developed for the detection of antipneumococcal antibodies. This was
accomplished by developing a different chemical procedure utilizing 3-aminopropyl trimethoxysilane and cyanuric chloride to
conjugate pneumococcal cell wall polysaccharides to the optical fiber tips, and by improving the sensitivity of the photodetection
system. The lowest titer of antipneumococcal antibodies detected by the optical fiber was at a 1:819,200 dilution. The lowest
corresponding value by standard enzyme-linked immunosorbent assay was at a 1:98,415 dilution. It was concluded that the optical
immunosensor system is an accurate and sensitive method to detect antipneumococcal antibodies and may be an adequate tool
to monitor antibodies in specimens such as saliva and urine. 相似文献
88.
M.J. Corden J.D. Dowell J. Garvey M. Jobes I.R. Kenyon J. Mawson T. McMahon I.F. Corbett R.J. Esterling N.H. Lipman P.J. Litchfield K.C.T.O. Sumorok G. Alexander S. Dagan Y. Gnat E.H. Bellamy M.G. Green N. Harnew D.H. Thomas 《Nuclear Physics B》1978,136(1):77-94
Data on the charge-exchange reaction π?p → (π+π?π0)n have been taken at beam momenta of 12 and 15 GeV/c, using the CERN Omega Multiparticle Spectrometer. A partial-wave analysis has been made of the (3π)0 system. We observe both natural and unnatural spin-parity production. The natural parity states can be identified with established resonances. In addition a natural spin-parity enhancement is observed at a mass of about 2 GeV/c2 with JP = 4+ preferred. We have called this effect the A21 (2030). The unnatural spin-parity production found is consistent with reggeized Deck model predictions. No unambiguous A1 or A3 production is observed. 相似文献
89.
M.J. Corden J.D. Dowell J. Garvey M. Jobes I.R. Kenyon J. Mawson T. McMahon I.F. Corbett R.J. Esterling N.H. Lipman P.J. Litchfield K.C.T.O. Sumorok G. Alexander S. Dagan Y. Gnat E.H. Bellamy M.G. Green N. Harnew D.H. Thomas 《Nuclear Physics B》1978,138(2):235-252
Data on the reaction π?p → π+π?π0 have been taken at 12 and 15 GeV/c with the CERN Omega multiparticle spectrometer. In a 3-pion partial-wave analysis strong production of is observed. Total and differential cross sections are determined and density matrix elements presented as a function of t in the t- and s-channel frames. The energy dependence of A20 production is studied, and a comparison of production is made. 相似文献
90.
The cross-channel isospin amplitude is measured in the single reaction γn → ?0(pπ?) at 7.5 GeV assuming the ?0 dominance model. A low-mass enhancement is found for in the range of m(pπ?) of ~1.2 to ~1.7 GeV. The reaction strongly violates s-channel helicity conservation but is consistent with t-channel helicity conservation. The features are found to be very similar to those obtained in previous analyses of πp → π(Nπ) reactions. 相似文献