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Nuclear spin-spin relaxation of60Co and56Co in iron single crystals has been studied, using the three-pulse NMRON spin echo. A previously reported rapidT
2 in60CoFe is shown to have arisen from a modulation of the echo amplitude, caused by variations in the phase of the Larmor precession
relative to the applied rf field. A lower limit ofT
2∼0.2s is found in56Co56
Fe. Extension of this result to other CoFe samples is discussed. 相似文献
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Alcorta M Rehm KE Back BB Bedoor S Bertone PF Deibel CM DiGiovine B Esbensen H Greene JP Hoffmann CR Jiang CL Lighthall JC Marley ST Pardo RC Paul M Rogers AM Ugalde C Wuosmaa AH 《Physical review letters》2011,106(17):172701
The structure of (15)C, with an s(1/2) neutron weakly bound to a closed-neutron shell nucleus (14)C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction (15)C+(232)Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring (14)C+(232)Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for (15)C, while the cross sections for (14)C match the trends measured for (12,13)C. 相似文献
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Polymerization of acrylamide has been initiated by the photochemical reactions of the dianions of croconic acid (1,2-dihydroxycyclopentenetrione) and rhodizonic acid (1,2-dihydroxycyclohexenetetrone) in the presence of various acceptor molecules. Photoinitiation was most efficient with croconic acid where a maximum quantum yield for polymerization of 2 x 103 was observed in neutral solution. Kinetic studies using this initiator showed that the rate of polymerization was a linear function of the concentration of monomer and proportional to the square root of the light absorbed by the croconate dianion. The rate of initiation of radicals calculated from the rate of polymerization was compared with the rate of production of radicals calculated from previous studies of the photochemistry of the croconate dianion and the mechanism of photoinitiation is discussed. © 1992 John Wiley & Sons, Inc. 相似文献
28.
Westrup KC Gregório T Stinghen D Reis DM Hitchcock PB Ribeiro RR Barison A Back DF de Sá EL Nunes GG Soares JF 《Dalton transactions (Cambridge, England : 2003)》2011,40(13):3198-3210
The reversible thermochromic behaviour of homoleptic [{V(OR)(4)}(n)] complexes in solution [R = Pr(i) (product I), Bu(s) (B(s)), Nep (N) and Cy (C)] is accounted for the existence of an aggregation equilibrium involving dimeric and monomeric species in which vanadium(iv) is respectively five- and four-coordinate. Bulky R groups such as Bu(t) and Pe(t) (tert-pentoxide) prevent aggregation and therefore give rise to exclusively mononuclear compounds (B(t) and P(t), respectively) that are not thermochromic. The complexes and their temperature-dependent interconversion were characterised by single crystal X-ray diffractometry, magnetic susceptibility measurements and electronic, FTIR and EPR spectroscopies in a wide temperature range. Equilibrium constants and enthalpy and entropy changes for the dimerization reactions have been determined and compared with literature data. 相似文献
29.
Sperança A Godoi B Pinton S Back DF Menezes PH Zeni G 《The Journal of organic chemistry》2011,76(16):6789-6797
A series of 4-Se-(Te, S)-isochromenones and 3-substituted isochromenones were synthesized in good yields via FeCl(3)-mediated cyclization of alkynylaryl esters with different diorganyl dichalcogenides. This methodology was carried out at room temperature, using inexpensive and environmentally friendly iron salts as metallic source and under air atmosphere. The reaction showed to be tolerant to a range of substituents bonded into the aromatic ring of the diorganyl dichalcogenides as well as to alkyl groups directly bonded to the chalcogen atom. Alternatively, the cyclization reaction of 2-alkynylaryl esters with FeCl(3), in the absence of diorganyl dichalcogenide, gave the isochromenones without the chalcogen moiety in the structure. This approach proved to be highly regioselective, providing only six-membered ring products, once the possible five-membered products were not observed in any experiments. 相似文献
30.
Mathematics and Financial Economics - We derive the optimal portfolio for an investor with increasing relative risk aversion in a complete continuous-time securities market. The IRRA assumption... 相似文献