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排序方式: 共有134条查询结果,搜索用时 359 毫秒
1.
D. Bisello G. Busetto A. Castro M. Nigro M. Penzo L. Pescara M. Posocco P. Sartori L. Stanco Z. Ajaltouni A. Falvard J. Jousset B. Michel J. C. Montret A. Antonelli R. Baldini A. Calcaterra G. Capon M. Schioppa J. -E. Augustin G. Cosme F. Couchot B. Dudelzak F. Fulda G. Grosdidier B. Jean-Marie S. Jullian D. Lalanne V. Lepeltier F. Manè C. Paulot R. Riskalla Ph. Roy G. Szklarz DM Collaboration 《Zeitschrift fur Physik C Particles and Fields》1988,39(1):13-19
Thee + e ?→K + K ? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ± form factor |F F ±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment. 相似文献
2.
Trost BM Shen HC Pinkerton AB 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(10):2341-2349
Catalyzed by ruthenium trisacetonitrile hexafluorophosphate 4, the Alder-ene type reaction of alkenes and internal alkynes provides an effective way to synthesize trisubstituted alkenes. Unlike most typical olefination protocols, this reaction is atom economical, and affords trisubstituted alkenes with defined olefin geometry. The regioselectivity can be explained invoking a steric argument based on the proposed mechanism. The first C-C bond formation generally involves sterically less hindered carbons of the alkenes and alkynes. Modest to very high regioselectivity can be achieved depending on the steric difference of the two substituents of alkynes. 相似文献
3.
The high-yield synthesis of 2-trimcthylsilylbenzothiazole is described, and the labile nature of this silicon-helerocyclic bond is proved when cleavage is affected by aldehydes, acid halides, chloro-formates and anhydrides. Justification for this unusual reactivity and further insight into the reaction mechanism is offered. 相似文献
4.
Hydrogen desorption exceeding ten weight percent from the new quaternary hydride Li3BN2H8 总被引:3,自引:0,他引:3
Pinkerton FE Meisner GP Meyer MS Balogh MP Kundrat MD 《The journal of physical chemistry. B》2005,109(1):6-8
Mobile applications of hydrogen power have long demanded new solid hydride materials with large hydrogen storage capacities. We report synthesis of a new quaternary hydride having the approximate composition Li(3)BN(2)H(8) with 11.9 wt % theoretical hydrogen capacity. It forms by reacting LiNH(2) and LiBH(4) powders in a 2:1 molar ratio either by ball milling or by heating the mixed powders above 95 degrees C. This new quaternary hydride melts at approximately 190 degrees C and releases > or =10 wt % hydrogen above approximately 250 degrees C. A small amount of ammonia (2-3 mol % of the generated gas) is released simultaneously. Preliminary calorimetric measurements suggest that hydrogen release is exothermic and, hence, not easily reversible. 相似文献
5.
6.
Jean-Marc Tornare Pierre Vogel A. Alan Pinkerton Dieter Schwarzenbach 《Helvetica chimica acta》1985,68(8):2195-2215
Stereoselective synthesis of 2-methylidene-3-[(Z)-(2-nitrophenylsulfenyl)methylidene]-7-oxabicyclo[2.2.1]-heptane ( 16 ), 1,4-epoxy-1,2,3,4-tetrahydro-5,8-dimethoxy-2-methylidene-3-[(Z)-(2-nitrophenylsulfenyl)methylidene]anthracene ( 18 ), and 1,4-epoxy-1,2,3,4-tetrahydro-5,8-dimethyoxy-2-methylidene-3-[(Z)-(phenylsulfenyl)-methylidene]anthracene ( 19 ) are presented. The Diels-Alder additions of these S-substituted dienes and those of 2,5-dimethylidene-3,6-bis{[(Z)-(2-nitrophenyl)sulfenyl]methylidene}-7-oxabicyclo[2.2.1]heptane ( 17 ) have been found to be face selective and ‘ortho’ regiospecific. The face selectivity depends on the nature of the dienophile. It is exo-face selective with bulky dienophiles such as ethylene-tetracarbonitrile (TCNE) and 2-nitro-1-butene and endo-face selective with methyl vinyl ketone, methyl acrylate, and 3-butyn-2-one. In the presence of a Lewis acid, the face selectivity of the Diels-Alder reaction can be reversed. The addition of the first equivalent of a dienophile to tetraene 17 is at least 100 times faster than the addition of the second equivalent of the same dienophile to the corresponding mono-adduct. The X-ray structure of the crystalline bis-adduct 43 , a 7-oxabicyclo[2.2.1]hepta-2,5-diene system annellated to two cyclohexene rings, resulting from the successive additions of methyl acrylate and methyl vinyl ketone to tetraene 17 is presented. Only one of the two endocyclic double bonds of the 7-oxabicyclo[2.2.1]hepta-2,5-diene deviates from planarity, the substituents bending towards the endo face by 5.7°. 相似文献
7.
Nuclear emulsions processed in discriminating developers, intended to suppress small latent image sites, exhibit supralinear sensitometric blackness-exposure curves, whose character varies according to developing time, concentration, and composition, yielding hittedness ranging from 1 to 8, singly and in combination. These emulsion-processing combinations display the phenomena called ion-kill (sensitization by the transit of a single charged particle) and gamma- kill (sensitization by the overlap of secondary electron paths, whether from x-rays or from the delta-rays of heavy ions) in radiobiology. Here emulsions are blackened by x-rays when these same plates reveal no electron tracks, or no alpha-particle tracks, or even no fission fragment tracks. The supralinearity of the emulsion response to x-rays, and the consequent suppression of low LET radiations suggest that these materials have the potential to mimic the response of biological systems to particulate radiations of different charge and speed. 相似文献
8.
9.
Pinkerton RG Barberi EA Menon RS 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(1):151-156
The use of multiple radiofrequency (RF) surface coil elements has applications in both fast parallel imaging and conventional imaging techniques. Through implementation of a simple magnetic decoupling network, 50 Omega matching can be achieved in both the transmitter and receiver chains, enabling the use of conventional RF power amplifiers and preamplifiers for transceive applications. Unlike phased array coil arrangements using low impedance preamplifiers for decoupling, the noise correlation between 50 Omega coils decoupled with discrete components has not been characterized. We have measured the dependence of coil quality factor (Q-factor) and noise correlation on coil separation and shown these quantities to be consistent with theoretical arguments, at least at 4 T (170 MHz). Our results suggest that a coil system for transmission and reception of NMR signals with 50 Omega coils can be built to take advantage of all the benefits of conventional array coils and with the added advantages of using conventional amplifiers. 相似文献
10.
B M Trost A B Pinkerton F D Toste M Sperrle 《Journal of the American Chemical Society》2001,123(50):12504-12509
The synthesis of 1,1-disubstituted alkenes typically involves reactions that lack atom economy such as olefination protocols. The use of various ruthenium complexes to effect the addition of terminal alkynes to alkenes is explored as an atom economical strategy. Two new ruthenium complexes have been discovered that effect this reaction at ambient temperature, cyclopentadienylruthenium (triphenylphosphine) camphorsulfonate and cyclopentadienylruthenium tris(acetonitrile) hexafluorophosphate. Using these complexes as catalysts, reactions proceed at ambient temperature in acetone or DMF, respectively. Regioselectivity favoring the formation of a 1,1-disubstituted over a 1,2-disubstituted alkene typically ranges from 9:1 to >25:1. The reaction demonstrates extraordinary chemoselectivity-even di- and trisubstituted alkenes such as present in the products do not compete with the starting monosubstituted alkene. Free hydroxyl groups as well as silyl and PMB ethers are tolerated as are ketones, esters, and amides. The mechanism of the reaction is believed to invoke formation of a metallacyclopentene. To account for the chemo- and regioselectivity, the initial formation of the metallacycle is believed to be reversible. While formation of the 2,5-disubstituted ruthenacyclopentene, which produces the linear product, is believed to be kinetically preferred, the rate of beta-hydrogen elimination from the 2,4-disubstituted ruthenacyclopentene, which produces the branched product, is believed to be faster. Thus, the competition between the rate of beta-hydrogen elimination and cycloreversion rationalizes the results. 相似文献