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71.
Giovanelli E Leroux S Moisan L Carreyre H Thuéry P Buisson DA Meddour A Coustard JM Thibaudeau S Rousseau B Nicolas M Hellier P Doris E 《Organic letters》2011,13(15):4116-4119
Detailed investigations on one of the key steps of the superacidic fluorination of Vinca alkaloids that is the origin of C20' activation are reported. While two different pathways can be envisioned for the emergence of the transient secondary carbocationic intermediate, isotopic labeling experiments unambiguously revealed the involvement of a 1,2-hydride shift mechanism. 相似文献
72.
Köhler J Hemberger P Fischer I Piani G Poisson L 《The journal of physical chemistry. A》2011,115(50):14249-14253
The ultrafast dynamics of isolated 9-fluorenone was studied by femtosecond time-resolved photoionization and photoelectron spectroscopy. The molecule was excited around 264-266 nm into the S(6) state. The experimental results indicate that the excitation is followed by a multistep deactivation. A time constant of 50 fs or less corresponds to a fast redistribution of energy within the initially excited manifold of states, i.e., a motion away from the Franck-Condon region. Internal conversion to the S(1) state then proceeds within 0.4 ps. The S(1) state is long-lived, and only a lower bound of 20 ps can be derived. In addition, we computed excited state energies and oscillator strengths by TD-DFT theory, supporting the interpretation of the experimental data. 相似文献
73.
Letp be a prime and denote byA the modp Steenrod algebra. We determine the indecomposableA-module summands ofH*((ℤ/p))
d
;F
p
which admit the structure of an unstableA-algebra. In fact, it turns out that this is equivalent to the problem of determining those indecomposableA-module summands which arise as the modp cohomology of a space (or even a classifying space of a finite group). We reduce this problem to one in modular representation
theory, namely for whichd andp is the projective cover of the trivial one dimensional GL(d,F
p
) representationF
p
a permutation module. Our solution of this latter problem makes use of the classification of subgroups of GL(d,F
p
) acting transitively on (F
p
)
d
\{0} and hence depends on the classification of finite simple groups (on Feit-Thompson's odd order theorem ifp=2). 相似文献
74.
Yvon Pointud Claude Bernard Sébastien Touzain Lionel Astier Béatrice Sabatier Jean Juillard 《Journal of solution chemistry》1997,26(5):479-495
The standard Gibbs functions, enthalpies, and entropies for the formation of the complexes of monensin acid with monovalent
metal cations in acetonitrile were obtained using various methods (conductometry, potentiometry, and calorimetry). Complexation
is appreciable (from 2.0 to 4.5 in terms of association constant logarithm) and controlled mainly by the enthalpic effect.
Comparison with formation of the corresponding neutral complexes permits a comparison to the process of monensin mediated
transport of cation in membranes. A two-step process involving first the formation of the acidic complex is suggested. 相似文献
75.
Summary. The paper is devoted to the construction of a higher order Roe-type numerical scheme for the solution of hyperbolic systems
with relaxation source terms. It is important for applications that the numerical scheme handles both stiff and non stiff
source terms with the same accuracy and computational cost and that the relaxation variables are computed accurately in the
stiff case. The method is based on the solution of a Riemann problem for a linear system with constant coefficients: a study
of the behavior of the solutions of both the nonlinear and linearized problems as the relaxation time tends to zero enables
to choose a convenient linearization such that the numerical scheme is consistent with both the hyperbolic system when the
source terms are absent and the correct relaxation system when the relaxation time tends to zero. The method is applied to
the study of the propagation of sound waves in a two-phase medium. The comparison between our numerical scheme, usual fractional
step methods, and numerical simulation of the relaxation system shows the necessity of using the solutions of a fully coupled
hyperbolic system with relaxation terms as the basis of a numerical scheme to obtain accurate solutions regardless of the
stiffness.
Received October 7, 1994 / Revised version received September 27, 1995 相似文献
76.
Monika Kuemmel Cédric Boissière Lionel Nicole Christel Laberty-Robert Clément Sanchez David Grosso 《Journal of Sol-Gel Science and Technology》2008,48(1-2):102-112
TiO2, Al2O3, and ZrO2 patterns composed of ordered nano motifs of various morphologies (i.e. perforations (craters), rings, canyons, wires, dots, or channels) with typical lateral dimensions of less than 40 nm and thickness below 15 nm are presented. Simple chemical solution deposition (CSD) of molecular inorganic precursors and commercial block copolymers was used to create patterns on several substrate surfaces (bare, hydrophobized or gold covered silicon wafers and ITO). Self-assembly during evaporation and subsequent stabilization at 500 °C leads to the various nanostructures. Compared to other techniques for surface nano patterning, the present method has the advantage of being cheap, reproducible and easy to scale up and does not require specialized equipment. The type, dimension, and organization of these motifs were assessed by AFM, FE-SEM, spectroscopic ellipsometry, and GI-SAXS and are shown to depend on the conditions of preparation. Usage as model surfaces for modelling of wetting properties and as nanoelectrode arrays were investigated. 相似文献
77.
Comparison of the lattice mode region of the low-temperature Raman spectrum of MCH and MCH-d14 under various cooling rates shows that there are two crystalline modifications. The molecular mode region frequencies however, remain invariant to cooling rate suggesting a single molecular conformation for both crystalline phases. 相似文献
78.
Lionel R. Milgrom 《Polyhedron》1985,4(9):1661-1664
1H and 13C NMR spectra of the title compound are reported and peaks assigned by comparison with the free-base porphyrin. Long-range spin—spin coupling is observed between platinum and the macrocyclic protons and carbon atoms. Meso-protons are assigned from line-broadening observed for three of the peaks, possibly caused by residual coupling of these protons to the pyrrole β-protons. Allylic coupling of the pyrrole β-protons to adjacent methyl groups is also noted, and supports the tautomeric model of an 18-atom delocalisation pathway around the macrocycle. The 1H NMR spectrum of the title compound is more concentration-dependent than that of the free-base porphyrin and probably reflects additional macrocyclic interactions via the platinum atoms. 相似文献
79.
80.
Dr. Lionel Weiss 《Probability Theory and Related Fields》1968,10(3):193-197
Summary
X
1,...,X
n
are independent random variables, identically distributed over the unit interval, with common probability density function 1 + r(x)/n
for all sufficiently large n, where is a positive constant,
and |r(x)| <D. V
1, ..., V
n+1 are the sample spacings generated by X
1,..., X
n
. It is shown that in many cases, the asymptotic joint distribution of homogeneous functions of V
1,..., V
n+1 can be found directly from the asymptotic joint distribution of homogeneous functions of independent exponential random variables.Research supported by NSF Grant GP 3783. 相似文献