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61.
62.
In this paper, we perform an analytical and numerical study of the extreme values of specific observables of dynamical systems possessing an invariant singular measure. Such observables are expressed as functions of the distance of the orbit of initial conditions with respect to a given point of the attractor. Using the block maxima approach, we show that the extremes are distributed according to the generalised extreme value distribution, where the parameters can be written as functions of the information dimension of the attractor. The numerical analysis is performed on a few low dimensional maps. For the Cantor ternary set and the Sierpinskij triangle, which can be constructed as iterated function systems, the inferred parameters show a very good agreement with the theoretical values. For strange attractors like those corresponding to the Lozi and He?non maps, a slower convergence to the generalised extreme value distribution is observed. Nevertheless, the results are in good statistical agreement with the theoretical estimates. It is apparent that the analysis of extremes allows for capturing fundamental information of the geometrical structure of the attractor of the underlying dynamical system, the basic reason being that the chosen observables act as magnifying glass in the neighborhood of the point from which the distance is computed. 相似文献
63.
Davide Addona 《Semigroup Forum》2013,87(3):509-536
We consider the nonautonomous Ornstein-Uhlenbeck operator in some weighted spaces of continuous functions in $\mathbb{R}^{N}$ . We prove sharp uniform estimates for the spatial derivatives of the associated evolution operator P s,t , which we use to prove optimal Schauder estimates for the solution to some nonhomogeneous parabolic Cauchy problems associated with the Ornstein-Uhlenbeck operator. We also prove that, for any t>s, the evolution operator P s,t is compact in the previous weighted spaces. 相似文献
64.
65.
We consider an elliptic operator of second order with Dirichlet boundary
conditions in a cylindrical domain. We show that a suitable interpretation of this
operator in a certain space of continuous functions vanishing on the boundary is
the infinitesimal generator of an analytic semigroup in the space of continuous
functions. We prove several inclusions of the domain of the infinitesimal generator
and of the real interpolation spaces between this domain and the basic space of
continuous functions. 相似文献
66.
The direct numerical simulation (DNS) of the Taylor–Couette flow in the fully turbulent regime is described. The numerical method extends the work by Quadrio and Luchini [M. Quadrio, P. Luchini, Eur. J. Mech. B/Fluids 21 (2002) 413–427], and is based on a parallel computer code which uses mixed spatial discretization (spectral schemes in the homogeneous directions, and fourth-order, compact explicit finite-difference schemes in the radial direction). A DNS is carried out to simulate for the first time the turbulent Taylor–Couette flow in the turbulent regime. Statistical quantities are computed to complement the existing experimental information, with a view to compare it to planar, pressure-driven turbulent flow at the same value of the Reynolds number. The main source for differences in flow statistics between plane and curved-wall flows is attributed to the presence of large-scale rotating structures generated by curvature effects. 相似文献
67.
Davide L. Ferrario 《Archive for Rational Mechanics and Analysis》2006,179(3):389-412
Periodic and quasi-periodic solutions of the n-body problem can be found as minimizers of the Lagrangian action functional restricted to suitable spaces of symmetric paths.
The main purpose of this paper is to develop a systematic approach to the equivariant minimization for the three-body problem
in three-dimensional space. First we give a finite complete list of symmetry groups fitting to the minimization of the action,
with the property that any other symmetry group can be reduced to be isomorphic to one of these representatives. A second
step is to prove that the resulting (local and global) symmetric action-minimizers are always collisionless (when they are
not already bound to collisions). Furthermore, we prove some results which address the question of whether minimizers are
planar or non-planar; as a consequence of our theory we will give general criteria for a symmetry group to yield planar or
homographic minimizers (either homographic or not, as in the Chenciner-Montgomery eight solution). On the other hand we will
provide a rigorous proof of the existence of some interesting one-parameter families of periodic and quasi-periodic non-planar
orbits. These include the choreographic Marchal's P12 family with equal masses – together with a less-symmetric choreographic family (which anyway probably coincides with the
P12 family). 相似文献
68.
Davide Toniolo Aurélien R. Willauer Dr. Julie Andrez Yan Yang Dr. Rosario Scopelliti Prof. Laurent Maron Prof. Marinella Mazzanti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(33):7831-7834
The activation of CS2 is of interest in a broad range of fields and, more particularly, in the context of creating new C−C bonds. The reaction of the dinuclear ytterbium(II) complex [Yb2L4], 1 , [L=(OtBu)3SiO−] with carbon disulfide led to the isolation of unprecedented reduction products. In particular, the crystallographic characterization of complex [Yb2L4(μ-C2S2)], 2 , provided the first example of an acetylenedithiolate ligand formed from metal reduction of CS2. Computational studies indicated that this unprecedented reactivity can be ascribed to the unusual binding mode of CS22− in the isolated “key intermediate” [Yb2L4(μ-CS2)], 3 , which results from the dinuclear nature of 1 . 相似文献
69.
We investigate the thermal conductivity of single-wall carbon nanotubes (SWCNT) either isolated or in contact with external media by using equilibrium molecular dynamics and the Boltzmann transport equation. We show that, contrary to existing controversies, both methods yield a finite value of the thermal conductivity for infinitely long tubes, as opposed to the case of 1D, momentum-conserving systems. Acoustic and flexure modes with mean free paths of the order of a few microns are identified as major contributors to the high value of SWCNT conductivity. We also find that the interaction with an external medium may substantially decrease the lifetime of the low-frequency vibrations, reducing the thermal conductivity by up to 2 orders of magnitude. 相似文献
70.
Roberta Sanna Davide Sanna Valeria Alzari Daniele Nuvoli Sergio Scognamillo Massimo Piccinini Massimo Lazzari Emilia Gioffredi Giulio Malucelli Alberto Mariani 《Journal of polymer science. Part A, Polymer chemistry》2012,50(19):4110-4118
Thermoresponsive poly(N‐vinylcaprolactam) nanocomposite hydrogels containing graphene were successfully prepared by frontal polymerization. High concentration of graphene (5.0 mg/mL) was obtained by direct graphite sonication in the self‐same liquid monomer, thus avoiding any chemical manipulation and obtaining “real” graphene as nanofiller instead of one of its more or less oxidized derivative, which is what generally reported in published reports. Furthermore, the corresponding nanocomposites were obtained without using any solvent to be eventually removed. The materials were fully characterized by RAMAN, SEM, and TEM, and their swelling behavior and rheological properties were investigated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献