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991.
For a given convex body K in
\Bbb R3{\Bbb R}^3
with C
2 boundary, let P
c
n
be the circumscribed polytope of minimal volume with at most n edges, and let P
i
n
be the inscribed polytope of maximal volume with at most n edges. Besides presenting an asymptotic formula for the volume difference as n tends to infinity in both cases, we prove that the typical faces of P
c
n
and P
i
n
are asymptotically regular triangles and squares, respectively, in a suitable sense. 相似文献
992.
993.
994.
995.
The Suzuki cross‐coupling reaction of various bromine‐containing substrates and phenylboronic acid in toluene at 90 °C on a Pd(AcO)2Py2 catalyst supported on an Mg? Al hydrotalcite, using K2CO3 as the base, was studied. The conversion and selectivity results obtained for many of the substrates were excellent and similar to those provided by more active or even homogeneous catalysts. The reactions of aryl polybromides and phenylboronic acid gave the corresponding polyaromatic compounds in variable yields depending on the particular substrate. Arylation occurred in a consecutive manner by substitution of the different Br atoms. ICP‐MS measurements of the palladium content of the catalyst performed prior to and after the reaction revealed that part of the metal is incorporated into the bulk solution; therefore, the catalytic process is not purely heterogeneous. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
996.
997.
998.
999.
We give an intrinsic characterization of an operator K recently introduced for relating the Lagrangian and Hamiltonian constraints and describing the time evolution of functions in T
*Q in terms of those of TQ. Its most remarkable properties are also studied. 相似文献
1000.
Michal Korenko Marián Kucharík Jozef Vincenc Oboňa Dušan Janičkovič Rosa Córdoba José María De Teresa Blanka Kubíková 《Helvetica chimica acta》2008,91(7):1389-1399
The rapid‐solidification processing (by a cooling rate of 105–106 K/s) was used for the preparation of deeply undercooled cryolite/alumina (Na3AlF6/Al2O3) melts. We found a mass of nanotubes on the surface of these undercooled melts. The nanotubes were preferentially located on the defect places of the surface with the following approximate dimensions: base≈100×100 nm, length≈1000 nm. The solidified samples with the nanotubes on the surface were analyzed by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and infrared spectroscopy (IR). 相似文献