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991.
992.
993.
On Metastability in FPU 总被引:1,自引:0,他引:1
We present an analytical study of the Fermi–Pasta–Ulam (FPU) α–model with periodic boundary conditions. We analyze the dynamics corresponding to initial data with one low frequency Fourier
mode excited. We show that, correspondingly, a pair of KdV equations constitute the resonant normal form of the system. We
also use such a normal form in order to prove the existence of a metastability phenomenon. More precisely, we show that the
time average of the modal energy spectrum rapidly attains a well defined distribution corresponding to a packet of low frequencies
modes. Subsequently, the distribution remains unchanged up to the time scales of validity of our approximation. The phenomenon
is controlled by the specific energy. 相似文献
994.
Francesco Costantino 《Geometriae Dedicata》2006,121(1):89-111
We provide sufficient conditions assuring that a suitably decorated 2-polyhedron can be thickened to a compact four-dimensional
Stein domain. We also study a class of flat polyhedra in 4-manifolds and find conditions assuring that they admit Stein, compact
neighborhoods. We base our calculations on Turaev’s shadows suitably “smoothed”; the conditions we find are purely algebraic
and combinatorial. Applying our results, we provide examples of hyperbolic 3-manifolds admitting “many” positive and negative
Stein fillable contact structures, and prove a four-dimensional analog of Oertel’s result on incompressibility of surfaces
carried by branched polyhedra.
相似文献
995.
996.
We study the analytic singularities of viscosity solutions of equations of eikonal type and obtain that the analytic singular
support of these functions has an analytic stratification. The singular support can be identified with the cut locus of the
distance to the boundary of an open set, when the interior is equipped with a degenerate Riemannian metric. We apply the result
to elliptic equations as well as to model operators of Grušin type. 相似文献
997.
998.
J. Lub D. J. Broer M. E. Martinez Antonio G. N. Mol 《Liquid crystals》1998,24(3):375-379
A nematic liquid crystal material containing a mercapto group and an olefinic group was synthesized. Photopolymerization of this compound in the liquid crystalline state resulted in a liquid crystalline main chain polymer which showed a relatively high birefringence. Due to scattering, the material had a low transmission at ambient temperatures. 相似文献
999.
1000.
Simona Bronco Giambattista Consiglio Silvia Di Benedetto Matthias Fehr Felix Spindler Antonio Togni 《Helvetica chimica acta》1995,78(4):883-886
Cationic Pd-complexes modified by dicyclohexyl{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}phosphine ( 1a ) give very active catalytic systems for the regioregular isotactic specific copolymerization of propene with CO. Other alk-1-enes also give stereoregular and regioregular copolymers, even if with lower productivity. The copolymers are isolated as poly(4-alkyl-tetrahydrofuran-2,2,5,5-tetrayl-2-oxy-2-methylenes) B in the solid state and give the isomeric poly(2-alkyl-1-oxopropane-1,3-diyls) A by dissolution in (CF3)2CHOH. Solid polymer A (R = Et) is formed back at least partially when the dissolved material is reprecipitated from MeOH. The use of the related (ferrocenyl)diphosphine ligands 1b ? e and 2 as the catalyst modifier shows that the presence of both elements of chirality and of large substituents on the P-atoms of the ligand is necessary to achieve good stereocontrol, and that the large difference in basicity between the two P-atoms is probably the reason for the good catalytic activity. 相似文献