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Jean Senegas Michel Pezat Jean Pierre Darnaudery Bernard Darriet 《Journal of Physics and Chemistry of Solids》1981,42(1):29-35
Wide line and pulsed NMR studies are reported for MgH2; and Mg2NiH4 hydrides at 79 and 30 MHz in the temperature range between 100 and 500 K. Line shape data confirm a rutile type structure for MgH2, and lead to the evaluation that 97% of the hydrogen is present in this phase, the remainder being in solid solution MgHx, (x<0.04).Mg2NiH4 shows a Gaussian line, whose peak-to-peak width decreases from 6.16 to 4.28 G in the range 320–365 K. From 365 to 480 K the spectrum shows a second, narrower, line (0.85 G), implying that approximately 7% of the protons have migrated from their initial position to energetically less stable sites. The thermal behaviour of the T1 and T2 relaxation times shows a dramatic variation in the 320–370 K temperature range in connection with the change of the proton localization. Relaxation mechanisms can be attributed mainly to conduction electron-nucleus interactions. With rising temperature, diffusion mechanisms are also involved. A diffusion activation energy of about 0.35 eV has been determined, with a diffusion coefficient 3.45 × 10?8 < D < 4.6 × 10?8 cm2/s. 相似文献
254.
The enthalpies of dissolution and dilution of LiBH4 and LiAlH4 in THF have been determined.Dissolutions are exothermic. The endothermic dilution of LiAlH4 suggests for this compound, either a dissociation or an association equilibrium. 相似文献
255.
Bernard S. Kay 《Physics letters. [Part B]》1981,101(4):241-245
Classical gravity with higher derivatives, when coupled to the in-out matrix element of Tμν: (a) appears to be free from instabilities of the in-in theory; (b) may be considered as the “underlying classical theory” to Tomboulis' quantum gravity. I explain how these two facts may be adduced as evidence for the viability both of the former semi-classical approximation and of the latter approach to full quantum gravity. 相似文献
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[reactions: see text] Regioselective synthesis of 2,4,5- or 3,4,5-trisubstituted 2,3-dihydrofurans has been realized by using donor-acceptor cyclopropanes or by a Corey ylide reaction with alpha-sulfenyl-, alpha-sulfinyl-, or alpha-sulfonylenones. The method allowed a straightforward synthesis of the natural product calyxolane B. 相似文献
258.
Boullet J Sabourdy D Desfarges-Berthelemot A Kermène V Pagnoux D Roy P Dussardier B Blanc W 《Optics letters》2005,30(15):1962-1964
Coherent combining is demonstrated in a clad-pumped Yb-doped double-core fiber laser. A slope efficiency of more than 70% is achieved with 96% of the total output power in the fundamental mode of one of the two cores. This high combining efficiency is obtained when both cores are coupled via a biconical fused taper in a Michelson interferometer configuration. 相似文献
259.
Aubin C Bernard C Detar C Di Pierro M Freeland ED Gottlieb S Heller UM Hetrick JE El-Khadra AX Kronfeld AS Levkova L Mackenzie PB Menscher D Maresca F Nobes M Okamoto M Renner D Simone J Sugar R Toussaint D Trottier HD;Fermilab Lattice Collaboration;MILC Collaboration;HPQCD Collaboration 《Physical review letters》2005,95(12):122002
We present the first lattice QCD calculation with realistic sea quark content of the D+-meson decay constant f(D+). We use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). We obtain f(D+)=201+/-3+/-17 MeV, where the errors are statistical and a combination of systematic errors. We also obtain f(Ds)=249+/-3+/-16 MeV for the Ds meson. 相似文献
260.
Rosso and Green have shown how to embed the positive part Uq() of a quantum enveloping algebra Uq() in a quantum shuffle algebra. In this paper we study some properties of the image of the dual canonical basis B* of Uq() under this embedding . This is motivated by the fact that when is of type Ar, the elements of (B*) are q-analogues of irreducible characters of the affine Iwahori-Hecke algebras attached to the groups GL(m) over a p-adic field. 相似文献