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1.
A novel low temperature technique has been developed for the synthesis of celsian glass-ceramics. The technique involves ion exchange of zeolites, their subsequent heat treatment to form a glassy phase from which celsian is crystallized. Monoclinic celsian was produced at temperatures as low as 1000°C at heat treatment times of 6 h. 相似文献
2.
Zero-valent palladium precatalysts containing rigid bidentate bis(arylimino)acenaphthene ligands (shown schematically) facilitate the highly stereoselective homogeneous catalytic hydrogenation of alkynes to (Z)-alkenes. Internal, terminal, aryl-substituted, and cyclic alkynes are suitable substrates, as are some enynes, which are chemoselectively hydrogenated to dienes. E=CO(2)Me; R(1), R(2)=4-OCH(3), 4-CH(3), 2,6-(CH(3))(2). 相似文献
3.
Good -stereoselectivity is observed in the epoxidation of allylic silyl ethers with CF3CO3H, indicating a new type of hydrogen-bonded transition state. 相似文献
4.
The sensitivity of all ion trap mass spectrometry (ITMS) methods is dependent on the trapping efficiency of the instrument. For ITMS instruments utilizing external ion sources, such as laser desorption, trapping efficiency is known to depend on the phase and amplitude of the radio frequency (RF) potential applied to the ring electrode at the time of ion introduction. It is remarkable that, in a considerable body of literature, no consensus exists regarding the effects of these parameters on the efficacy of trapping externally generated ions. In this paper, a summary of the literature is presented in order to highlight significant discrepancies. New laser desorption ion trap mass spectrometry (LD-ITMS) data are also presented, from which conclusions are drawn in our effort to clarify some of the confusion. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
5.
The design, fabrication, and testing of photoelastic models of double-lap, multiple-pin connectors are discussed. Interest
is in the stresses in the inner laps. These stresses are determined by constructing models with photoelastic inner laps and
transparent-acrylic outer laps. The connectors have two pins, in tandem, parallel to the load direction. A photoelastic-isotropic
point is shown to permit the evaluation of load sharing between the two pins. A numerical scheme, utilizing the isochromatic-
and isoclinic-photoelastic data and a finite-difference representation of the planestress equilibrium equations, is used to
compute the stresses around the two pins. Representative stress distributions and stress-concentration factors are shown. 相似文献
6.
J.K. Han M.E. Hannah A. Piquette G.A. Hirata J.B. Talbot K.C. Mishra J. McKittrick 《Journal of luminescence》2012,132(1):106-109
This paper reports on the luminescence properties of mixtures of α- and β-(Sr0.97Eu0.03)2SiO4 phosphors. These phosphors were prepared by 3 different synthesis techniques: a modified sol–gel/Pechini method, a co-precipitation method and a combustion method. The structural and optical properties of these phosphors were compared to those of solid state synthesized powders. The emission spectra consist of a weak broad blue band centered near 460 nm and a strong broad green–yellow band centered between 543 and 573 nm depending on the crystal structure. The green–yellow emission peak blue-shifts as the amount of β phase increases and the photoluminescence emission intensity and quantum efficiency of the mixed phase powders is greater than those of predominant α-phase powders when excited between 370 and 410 nm. Thus, (Sr1?xEux)2SiO4 with larger proportion of the β phase are more promising candidates than single α-phase powders for use as a green–yellow emitting phosphor for near UV LED applications. Finally the phosphors prepared by the sol–gel/Pechini method, which have larger amount of β phase, have a higher emission intensity and quantum efficiency than those prepared by co-precipitation or combustion synthesis. 相似文献
7.
H. Burstin E. Katz E. H. Kadmer A. v. Philippovich A. Graf H. G. Botset I. I. Starosstin I. M. Abesgaus I. Blum D. S. McKittrick H. J. Henriques H. I. Wolff A. W. Trusty J. A. Eminow N. I. Plachuta L. L. Lanzewitzkaja E. Casirnir N. Dimitriu V. Salač J. Mühlbauer 《Analytical and bioanalytical chemistry》1941,121(1-2):65-70
8.
The synthesis of a C-6 hydroxy tricyclic sulfone was described with two key reactions: the Suzuki coupling and the regioselective and stereoselective cis ring opening of the epoxide. Overall, the 14-step synthesis was achieved in 2.1% yield. 相似文献
9.
H. Burstin E. Katz E. H. Kadmer A. v. Philippovich A. Graf H. G. Botset I. I. Starosstin I. M. Abesgaus I. Blum D. S. McKittrick H. J. Henriques H. I. Wolff A. W. Trusty J. A. Eminow N. I. Plachuta L. L. Lanzewitzkaja E. Casirnir N. Dimitriu V. Sala und J. Mühlbauer 《Fresenius' Journal of Analytical Chemistry》1941,121(1-2):65-70
Ohne Zusammenfassung 相似文献
10.
A new ligand capable of producing calcium-selective electrodes with excellent characteristics is presented. The ligand (1) is a calix[4]arene bearing phosphine oxide ligating groups on the lower rim and this is the first report that such ligands can discriminate in favour of calcium ions against magnesium ions and the alkali metal ions. This calcium selectivity is in complete contrast to the behaviour of the well-known calix[4]arene tetraester derivatives (such as 2) which are selective for sodium against other alkali metal ions and group II ions. Electrodes based on PVC membranes incorporating ligand 1 display almost nernstian slopes and excellent selectivity against common interferants, including magnesium (log K(Ca,Mg)(pot)). The electrodes have demonstrated effective lifetimes of at least 7 weeks (duration of the study) and very fast response times. 相似文献