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131.
A generalised Hohenberg–Kohn theorem is described in terms of the sign of the secondorder energy variation. Independently, it is also corroborated within the perturbation theoretical framework. An alternative formulation of the Hohenberg–Kohn theorem, based on the relationships involving the matrix representations of density functions and the Hamiltonian operator variations, is shown to extend the validity of the theorem to the excited states of the Hamiltonian operators possessing nondegenerate spectra. Finally, a connection with Brillouin's theorem when energy variation becomes stationary is also outlined. 相似文献
132.
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135.
We examine the robustness of ultrashort optical vortices propagating freely in the atmosphere. We first approximate the stability regions of femtosecond spinning pulses as a function of their topological charge. Next, we numerically demonstrate that atmospheric optical vortices are capable of conveying high power levels in air over hundreds of meters before they break up into filaments. 相似文献
136.
Stable polar oxide surfaces must be simultaneously electrostatically compensated and in thermodynamic equilibrium with the environment. As a paradigm, the MgO(111)-p(2x2) reconstructed surface is shown to involve combinations of Mg-covered terminations with peculiar insulating electronic structure, favored in O-poor conditions, and the O-terminated octopole, stabler in more O-rich environments. Such a picture, which could not have been foreseen by either experiments or simulations separately, goes beyond the Wolf model and reconciles the theory with the experimental data taken in variable thermodynamic conditions. 相似文献
137.
E.?DintwaEmail author M.?van?Zeebroeck E.?Tijskens H.?Ramon 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,39(1):77-85
The theory of elastic contact between two spherical bodies according to Hertz, Mindlin and others is used as a basis for an extension to include the contribution of the viscous effects to the total stress for viscoelastic spheres subjected to twisting moments. Expressions relating twisting moment to the radius of a stick region of the contact surface and the radius of the stick region to twist angle are derived. Two term power series truncations of the relations are then used to derive approximate expressions for torsional stiffness of the bodies. Validation of the model was by experiments utilising a rheometer device. Applications for the model in post-harvest agriculture include extraction of material surface properties for use in discrete element modelling of mechanical interactions of fruits and other spheroidal produce during machine handling.Received: 6 January 2004, Published online: 18 June 2004PACS:
46.35. + z Viscoelasticity, plasticity, viscoplasticity - 46.55. + d Tribology and mechanical contacts - 62.20.Dc Elasticity, elastic constants 相似文献
138.
Luis A.?CaffarelliEmail author Ki-Ahm?Lee Antoine?Mellet 《Archive for Rational Mechanics and Analysis》2004,172(2):153-190
This paper is concerned with a class of singular equations modelling the combustion of premixed gases in periodic media. The model involves two parameters: the period of the medium |L| and a singular parameter related to the activation energy. The existence of pulsating travelling fronts for fixed and |L| was proved by Berestycki & Hamel in [BH]. In the present paper, we investigate the behaviour of such solutions when
More precisely, we establish that pulsating travelling fronts behave like travelling waves, when the period |L| is small and . We also study the convergence of the solution, as goes to zero (and |L| is fixed), toward a solution of a free boundary problem. 相似文献
139.
140.
Antoine?AyacheEmail author Murad S.?Taqqu 《Journal of Fourier Analysis and Applications》2003,9(5):451-471
Consider the fractional Brownian motion process $B_H(t), t\in [0,T]$,
with parameter $H\in (0,1)$.
Meyer, Sellan and Taqqu have developed
several random wavelet representations for
$B_H(t)$, of the form $\sum_{k=0}^\infty
U_k(t)\epsilon_k$ where $\epsilon_k$ are Gaussian random
variables and where the functions $U_k$ are not random. Based on the
results of Kühn and Linde, we say that the
approximation $\sum_{k=0}^n U_k(t)\epsilon_k$ of $B_H(t)$
is optimal if
$$
\displaystyle
\left( E \sup_{t\in [0,T]} \left| \sum_{k=n}^\infty U_k(t)
\epsilon_k\right|^2 \right)^{1/2} =O
\left( n^{-H} (1+\log n)^{1/2} \right),
$$
as $n\rightarrow\infty$. We show that the random wavelet
representations given in Meyer, Sellan and
Taqqu are optimal. 相似文献