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61.
Computer calculations of the kinetics of the ferric ion catalyzed decomposition of H2O2 by Walling and Weil are not in contradiction to the “complex mechanism.” The examination of their results reveals that their simulations correspond to the terminal state of the system in which the secondary complex between Fe3+ and H2O2 becomes stabilized.  相似文献   
62.
The pyrolysis of purified celluloses in air at 251°C was studied. The pyrolysis was found to obey first-order kinetics, and the rate constants correlated with the crystallinities, orientations and accessibilities of the samples. The results are interpreted in terms of an oxygen-catalyzed decomposition, with the accessibility of oxygen to the cellulose determining the rate of pyrolysis. The production of levoglucosan under conditions approaching combustion was shown to be a function of the crystallinity and orientation of cellulose. Some levoglucosan appears to be produced from the less ordered regions.  相似文献   
63.
A generalization of the matrix-tree theorem   总被引:1,自引:0,他引:1  
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64.
We show that for a composite fermion of sufficiently small radius, the magnetic moment approaches the Dirac value corresponding to the overall charge and mass, regardless of the constituent values. This resolves a recently suggested difficulty in composite models of leptons and quarks.  相似文献   
65.
The behaviour of the synthetic (−)-16-(aminomethyl)eburnamenine (prepared from apovincamine) with formaldehyde was studied. Carrying out the reaction in acetic acid led to an original dimer, while in trifluoroacetic acid a 12-functionalized eburnamonine was isolated.  相似文献   
66.
The effects of orientation upon the pyrolysis of cellulose were investigated by using a series of rayon fibers which differed only in orientation. The initial weight loss seen in low-temperature vacuum pyrolysis is due to crosslinking in the less ordered regions and was shown to be a first-order reaction whose rate varies directly with the degree of orientation. The extent of this reaction decreases with increasing orientation and is directly related to the amount of char formed at higher temperatures. The bulk pyrolysis rate increases with increasing orientation. DSC, air pyrolysis rates, and levoglucosan formation were also studied.  相似文献   
67.
The NMR spectra of water adsorbed at various relative humidities on various cellulose ester membranes have been studied. Membranes of cellulose acetate (CA), cellulose triacetate (CTA), and cellulose acetate butyrate (CAB) were investigated. It was found that the resonance peak of a liquid imbibed in or adsorbed on membranes from high relative humidity is very sensitive to the angle between the membrane plane and the direction of the magnetic field, shifting 5–7 ppm to higher fields as the membrane plane is rotated from a perpendicular to a parallel position with respect to the direction of the external magnetic field. This phenomenon was found to be independent of the nature of the polymeric material (namely CA, CTA, or CAB), porosity of the membrane (varying from an “all bulk” dense sheet to an 80% porosity and 0.2 μm average pore size membrane), nature of the magnetic nuclei (H2O or D2O), intensity of the external magnetic field (60 Mcps or 100 Mcps), and nature of the liquid in the membrane (water, methanol, or n-hexane). It is therefore concluded that the dependence of the position of the resonance peak on the position of the membrane plane with respect to the external magnetic field, is a geometrical phenomenon due to the magnetic “bulk susceptibility” of the medium. Quantitative estimations of the magnitude of the diamagnetic susceptibility effect in a cylindrically rolled sheet are given. These estimates agree well with the experimentally observed “splittings.”  相似文献   
68.
Eight angular distributions measured for 18+, π?)18Ne(gs) across the Δ33 resonance show the details of the energy dependence of the reaction. At higher energies, the maximum is at q ? 0.85 fm?1, in agreement with simple sequential scattering models, but a lower energies it is at q ? 0.5 fm?1, with the transition occuring over a narrow energy range.  相似文献   
69.
The reaction 12C(t, p)14C has been investigated with an 18 MeV triton beam. Twenty energy levels of 14C were identified up to 13 MeV excitation. Angular distributions were measured and compared with DWBA calculations. A previously unreported 0+ level at 9.75 MeV was observed; it undoubtedly corresponds to the second predominantly sd shell 0+ state in 14C. Additional spin and parity assignments have been made in the present work: 9.81 MeV, (1?); 10.43 MeV, 2+; 10.50 MeV, (3?); 10.74 MeV, 4+; 11.40 MeV, 1?; 11.67 MeV, (1?); 11.73 MeV, (5?); 12.58 MeV, (2+, 3?); 12.87 MeV. 2+, 3?; and 12.96 MeV, (1?); none of which had a definite spin and parity assignment previously. Our results confirm the previous information on the level structure of 14C below 8.5 MeV. The cross section for the unnatural parity state at 7.34 MeV, Jπ = 2?, is well reproduced by a two-step reaction calculation. The results are compared with the predictions of a weak coupling model.  相似文献   
70.
The 1,4-dimethyl-, 1,2,4-trimethyl and 1,2,4,7-tetramethyl substituted 3,4-(o,o'-biphenylene) cyclopentadienone-dimers (6a6c) were prepared and found to undergo photochemically or thermally a 1,3-rearrangement to the centrosymmetrical diketones (11). Only the tetramethyl derivative (6a) undergoes at room temperature a fast, degenerate [3.3] Cope rearrangement with ΔG233 = 11.4 kcal mol.?1 All these dimers and rearrangement products appear not to dissociate to their monomers, but react with dienophiles to give the adducts (12, 13). A stepwise mechanism involving diradical intermediates (19) is invoked. The “mixed dimer” (14) was also prepared and studied. The steric and electronic effects determining the behaviour of these compounds are discussed.  相似文献   
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