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Stefano Lisini Daniel Matthes Giuseppe Savaré 《Journal of Differential Equations》2012,253(2):814-850
In this paper, we establish a novel approach to proving existence of non-negative weak solutions for degenerate parabolic equations of fourth order, like the Cahn–Hilliard and certain thin film equations. The considered evolution equations are in the form of a gradient flow for a perturbed Dirichlet energy with respect to a Wasserstein-like transport metric, and weak solutions are obtained as curves of maximal slope. Our main assumption is that the mobility of the particles is a concave function of their spatial density. A qualitative difference of our approach to previous ones is that essential properties of the solution – non-negativity, conservation of the total mass and dissipation of the energy – are automatically guaranteed by the construction from minimizing movements in the energy landscape. 相似文献
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Stefano Gialanella Elisa Possenti Daniel Chateigner Luca Lutterotti Francesco Marino 《Applied Physics A: Materials Science & Processing》2013,113(4):1101-1108
This study concerns the archaeometric characterization of two artefacts from the medieval site of San Rocco (Castelfranco Veneto, Italy). Both of them belong to a larger set of metallic objects, some being part of tomb ornaments belonging to two very well distinct periods of frequentation of the site. Both items are buckles and they have been selected as representative of two very well-known and established typologies. The older one, at the end of the sixth—beginning of the seventh century AD, is made of silver, although relicts of gold have been found. A number of relevant counterparts of this item have been found in different sites of the Longobard Italy. The main body of the second artefact (second half of the fourteenth century AD) consists of a bent strip of a copper rich alloy, coated on one side with a nearly continuous, decorated, gold layer. This is a so-called lyre-buckle, with a widespread diffusion not only in Italian, but also North European contexts. From the results of the analyses carried out using low-vacuum scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffractometry, information on manufacturing, gilding technology and materials have been obtained that will be an useful benchmark for the archaeometric characterization of similar items from selected collections. In this way, the already established typological affinity of these two classes of items will be extended to technological and materials aspects, also. 相似文献
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Fabio Frassetto Stefano Coraggia Siarhei Dziarzhytski Natalia Gerasimova Luca Poletto 《Journal of synchrotron radiation》2012,19(4):596-601
The design and the commissioning results of a portable and compact spectrometer for the high harmonics content characterization of the extreme‐ultraviolet radiation of FLASH (free‐electron laser in DESY, Hamburg, Germany) are presented. The instrument is a grazing‐incidence flat‐field spectrometer equipped with two variable‐line‐spaced gratings; it covers the 2–40 nm wavelength region with a spectral resolution in the 0.1–0.2% range. Both spectral and intensity fluctuations of the fundamental emission and the harmonics are monitored. 相似文献