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991.
Michael J. Begley Christopher B. Jackson Gerald Pattenden 《Tetrahedron letters》1985,26(28):3397-3400
Treatment of either the verticillenes (3), (6), (13) or (14) with Lewis acids fails to produce the corresponding taxane carbon framework (2), and instead only products, e.g. (8), (9), (16), of rearrangement of the epoxide rings in the substrates are obtained. 相似文献
992.
We improve an upper bound for the chromatic index of a multigraph due to Andersen and Gol'dberg. As a corollary we deduce that if no two edges of multiplicity at least two in G are adjacent, then χ′(G) ? Δ(G) + 1. In addition we generalize results concerning the structure of critical graphs due to Vizing and to Chetwynd and Hilton. 相似文献
993.
994.
995.
The adsorption of sulphur on two palladium/alumina catalysts, prepared from different precursors, has been investigated using [35S] H2S. 相似文献
996.
F. M. Harris P. J. Jackson J. A. Rontree W. J. Griffiths 《Journal of mass spectrometry : JMS》1992,27(3):261-269
Double-charge-transfer spectrometry was used to measure double-ionization energies to ground and electronically excited states of various chlorobenzenes. Since OH+ was the projectile ion used in these experiments, it is probable that triplet states of the dications were populated because of spin conservation in the double-electron-capture reactions which are the basis of this type of spectrometry. The lowest double-ionization energies for all the molecules studied are within ±0.3 eV of 25.9 eV, except that for 1,3-dichlorobenzene, which is at 26.6 eV. In general, double-ionization energies to three higher lying states (or groups of states) were measured for each molecule. The energies of these states are the same, within experimental uncertainties, for the three trichlorobenzenes, two tetrachlorobenzenes and pentachlorobenzene dications, suggesting that they have the same or very similar distributions of triplet-state energies. 相似文献
997.
A general theorem is obtained for the enumeration of permutations equivalent under cyclic rotation. This result gives the generating function as the logarithm of a determinant which arises in the enumeration of a related linear permutation enumeration. Applications of this theorem are given to a number of classical enumerative problems. 相似文献
998.
W.E. Kieser R.E. Azuma I. Berka K.P. Jackson A.B. McDonald H.B. Mak W. McLatchie 《Nuclear Physics A》1979,327(1):172-192
The resonance previously observed at Ex = 6241 keV in the reactions 17O(p, γ)18F and 14N(α, γ)18F has been found to be a closely separated doublet (ΔEx = 2.09±0.04 keV). Resonance strengths in 17O(p, γ)18F, 17O(p, α)14N and 14N(α, γ)18 have been measured and partial widths for the resonance states have been obtained. The doublet was further investigated by means of the 4He(14N, α)14N reaction using the differentially pumped gas target at CRNL. Analysis of these data using R-matrix theory yielded Jπ = 3? for both states and more precise values of the α-particle widths (Γα(lower) = 133 ±4 eV; Γα(upper) = 137 ±4 eV). The reduced α-particle widths and the E1 and M1 transition strengths indicate that the doublet arises from the nearly complete mixing of T = 0 and T = 1 eigenstates which in the absence of an isospin breaking interaction would have been separated by less than 40 eV. The α-particle scattering experiments included the Jπ = 1+ resonance at Ex = 6257 keV and yielded the new values of Γα = 580±12 eV and Γp = 25+35?25 eV. 相似文献
999.
A. Jànossy K. Holczer P.L. Hsieh C.M. Jackson A. Zettl 《Solid State Communications》1982,43(7):507-510
We have measured the low temperature dielectric constant ? of two similar quasi one-dimensional organic conductors, N-Me-iso Qn(TCNQ)2 and Qn(TCNQ)2. For N-Me-iso Qn(TCNQ)2 below 10 K, ? is independent of temperature and is frequency independent in the range 5 × 105 Hz to 9 × 109 Hz, within the 50% experimental uncertainty. Thus we believe the low temperature microwave dielectric constant to be a good approximation of the static value in this salt. For Qn(TCNQ)2 at low temperatures, the relation ? ∝ (c+c0)-2 holds, where c is the defect concentration and c0 is an effective defect concentration of the nominally pure material. This relation is predicted by the model of interrupted metallic strands with energy spacings larger than kT, and it indicates that electrons are strongly localized by defects along the conducting chains. 相似文献
1000.
A. Zettl C.M. Jackson A. Janossy G. Grüner A. Jacobsen A.H. Thompson 《Solid State Communications》1982,43(5):345-347
We report dc conductivity (σ) measurements on the linear chain compound NbS3. The temperature dependence of σ indicates a phase trànsition at TMI = 155 K with strong one-dimensional fluctuations above TMI. Below TMI the conductivity is strongly increasing with increasing electric field above a threshold field ET, and is also strongly frequency dependent. We argue that the nonlinear conductivity is due to sliding charge density waves. 相似文献