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41.
Alberto Bargagna Pietro Schenone Filippo Evangelisti 《Journal of heterocyclic chemistry》1979,16(1):93-96
The dipolar 1,4-cycloaddition of dichloroketene to N,N-disubstituted 3-amino-1-phenyl-2-propene-1-onesled directly to N,N-disubstituted 4-amino-3-chloro-6-phenyl-2H-pyran-2-ones only in the case of an usual aliphatic N,N-disubstitution. In the case of partial or full aromatic N-substitution, N,N-disubstituted 4-amino-3,3-dichloro-3,4-dihydro-6-phenyl-2H-pyran-2-ones were instead obtained, which were dehydrochlorinated with DBN to the corresponding 4-amino-3-chloro-6-phenyl-2H-pyran-2-ones. 相似文献
42.
Di Antonio M Doria F Mella M Merli D Profumo A Freccero M 《The Journal of organic chemistry》2007,72(22):8354-8360
Mild activation of water-soluble naphthalene diimides (NDIs) as bisalkylating agents has been achieved by base catalysis and by chemical and electrochemical reductions. NDI activation by a single electron reduction represents a novelty in the field of activatable electrophiles. Under mild reduction, induced by S2O4(2-) in aqueous solution, the resulting NDI radical anion (NDI*-) undergoes a monomolecular fragmentation to yield a new transient species, where the NDI radical anion is tethered to a quinone methide moiety. The latter still retains electrophilic properties, reacting with amines, thiols, and ethyl vinyl ether. Owing to the NDI recognition properties, these results represent the first step toward selective and bioactivatable cross-linking agents. 相似文献
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The M
α
energy which is usually minimized in branched transport problems among singular one-dimensional rectifiable vector measures
is approximated by means of a sequence of elliptic energies defined on more regular vector fields. The procedure recalls the
one of Modica-Mortola related to the approximation of the perimeter. In our context, the double-well potential is replaced
by a concave term. The paper contains a proof of Γ−convergence and numerical simulations of optimal networks based on that
previous result. 相似文献
46.
Jean-Michel Morel Filippo Santambrogio 《Archive for Rational Mechanics and Analysis》2010,195(2):499-531
A branched structure is observable in draining and irrigation systems, in electric power supply systems, and in natural objects
like blood vessels, the river basins or the trees. Recent approaches of these networks derive their branched structure from
an energy functional whose essential feature is to favor wide routes. Given a flow s in a river, a road, a tube or a wire, the transportation cost per unit length is supposed in these models to be proportional
to s
α with 0 < α < 1. The aim of this paper is to prove the regularity of paths (rivers, branches,...) when the irrigated measure
is the Lebesgue density on a smooth open set and the irrigating measure is a single source. In that case we prove that all
branches of optimal irrigation trees satisfy an elliptic equation and that their curvature is a bounded measure. In consequence
all branching points in the network have a tangent cone made of a finite number of segments, and all other points have a tangent.
An explicit counterexample disproves these regularity properties for non-Lebesgue irrigated measures. 相似文献
47.
Weak steady Mach reflections are numerically simulated using unstructured grids by means of either “shock-fitting” or “shock-capturing”
techniques. It is shown that shock-fitting allows using coarser meshes than those required by shock-capturing, since the latter
needs mesh refinement in the direction normal to the discontinuities, which is not needed using the former approach. The shock-fitted
solution is also free from the numerical disturbances that arise along the captured discontinuities and pollute the captured
solution in the smooth flowfield region. Finally, the shock-fitting solutions show the presence of a small region next to
the Mach stem and the reflected shock downstream of the triple point, characterized by very high gradients. 相似文献
48.
Chlorofluorocarbons and their substitutes are anthropogenic compounds strongly involved in global change phenomena. Therefore, their atmospheric mixing-ratios are monitored on a worldwide scale. In order to evaluate source strength of these compounds in Southern Europe, in 1999 a research activity, monitoring these compounds in the atmosphere of the Monte Cimone (MO, Italy) was started. Air samples, collected on a weekly base, were analyzed using a GC-MS methodology recently devised by our group. The reported results, obtained after eighteen months of observation, are relative to four fully halogenated halocarbons and four hydrogenated halocarbons. 相似文献
49.
50.
The Mössbauer spectra of iron (III) bis and tris dithiocarbamates containing the piperidylradical have been investigated at various temperatures. The tris chelate shows a quadrupole splitting decreasing when the sample is warmed up which indicates the presence of a Boltzmann spin equilibrium. The bis chelate yields a temperature-independent quadrupole splitting due to the lattice contribution.Work sponsored in part by G.N.S.M. and in part by C.N.R. 相似文献