U (lettre)

Résumé

Le U (prononcé /y/) est la et la voyelle de l'alphabet latin moderne. À l'origine, en latin, il n'existait pas et était représenté par le V. Origine Linguistique

API: Voyelle haute postérieure arrondie

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Épellation alphabet radio ** international : Uniform ** allemand : Ulrich ** français : Ursule ** police aux États-Unis : Union
En alphabet morse, la lettre U vaut « ··- »

Autres Voir aussi

Alphabet latin
υ (upsilon), lettre de l'alphabet grec

Catégorie:Lettre latine *

Source officielle

https://fr.wikipedia.org/wiki/U_(lettre)

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We study stationary max-stable processes {n(t): t is an element of R} admitting a representation of the form n(t) = max(i is an element of N) (U-i +Y-i(t)), where Sigma(infinity)(i=1) delta U-i is a Poisson point process on R with intensity e(-u)du, and Y1,Y2 are i.i.d. copies of a process {Y (t) : t is an element of R} obtained by running a Levy process for positive t and a dual Levy process for negative t. We give a general construction of such Levy-Brown-Resnick processes, where the restrictions of Y to the positive and negative half-axes are Levy processes with random birth and killing times. We show that these max-stable processes appear as limits of suitably normalized pointwise maxima of the form Mn(t) = max(i=1),...,n xi i (s(n) + t), where xi 1, xi 2... are i.i.d. Levy processes and sn is a sequence such that s(n) similar to clog n with c > 0. Also, we consider maxima of the form max(i=1),...,n Z(i) (t/log n), where Zi, Z2,... are i.i.d. Ornstein-Uhlenbeck processes driven by an alpha-stable noise with skewness parameter beta = -1. After a linear normalization, we again obtain limiting max-stable processes of the above form. This gives a generalization of the results of Brown and Resnick (1977) to the totally skewed a-stable case. (C) 2015 Elsevier B.V. All rights reserved.

Elsevier2015

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Electronic structure of KTi(SO4)(2)center dot H2O: An S=1/2 frustrated chain antiferromagnet

Goran Nilsen, Julian Piatek, Henrik Moodysson Rønnow

The compound KTi(SO4)(2)center dot H2O was recently reported as a quasi-one-dimensional spin-1/2 compound with competing antiferromagnetic nearest-neighbor exchange J(1) and next-nearest-neighbor exchange J(2) along the chain with a frustration ratio alpha = J(2)/J(1) approximate to 0.29 [G. J. Nilsen, H. M. Ronnow, A. M. Lauchli, F. P. A. Fabbiani, J. Sanchez-Benitez, K. V. Kamenev, and A. Harrison, Chem. Mater. 20, 8 (2008)]. Here, we report a microscopically based magnetic model for this compound derived from density functional theory (DFT) based electronic structure calculations along with respective tight-binding models. Our (LSDA+U-d) calculations confirm the quasi-one-dimensional nature of the system with antiferromagnetic J(1) and J(2), but suggest a significantly larger frustration ratio alpha(DFT) approximate to 0.94-1.4, depending on the choice of U-d and structural parameters. Based on transfer matrix renormalization group (TMRG) calculations we find alpha(TMRG) = 1.5. Due to an intrinsic symmetry of the J(1)-J(2) model, our larger frustration ratio alpha is also consistent with the previous thermodynamic data. To identify the frustration ratio alpha unambiguously, we propose performing high-field magnetization and low-temperature susceptibility measurements.

American Physical Society2013

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Improvements in short-circuit currents of micromprph solar cells are investigated, with respect of nano-imprinted textures to glass superstrate. 2-D U-like periodic textures are optimized by means of 3-D rigorous optical simulations. Simulations indicate potential for > 35 % improvements in JSCbot for the optimized U-like textures with high aspect ratio compared to state-of-the-art random textures.

2013

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