The essential oil of Thymbra capitata and its application as a biocide on stone and derived surfaces

Many chemicals used nowadays for the preservation of cultural heritage pose a risk to both human health and the environment. Thus, it is desirable to find new and eco-friendly biocides that can replace the synthetic ones. In this regard, plant essential oils represent effective alternatives to synthetic substances for the preservation of historical monuments. Thymbra capitata (syn. Thymus capitatus) is a medicinal and aromatic plant growing in the Mediterranean area and endowed with important pharmacological properties related to its essential oil. Among them, the antimicrobial ones make the T. capitata essential oil an ideal candidate for industrial applications; for instance, as biocide for the inhibition and elimination of biological patinas of cyanobacteria and green algae on historical monuments. In the present work, we studied the chemical composition of the essential oil from T. capitata growing in Malta by gas chromatography-mass spectrometry (GC/MS). The major volatile component is the phenolic monoterpene carvacrol (73.2%), which is capable of damaging the cytoplasmic membrane and to interfere both in the growth curve and in the invasive capacity, though the contribution of minor components γ-terpinene and p-cymene cannot be disregarded. For the oil application on the stone surface, Pickering emulsions systems were prepared with an essential oil/water 1:3 mass ratio stabilized with kaolinite at 4 mass% in the presence of Laponite®; this allowed to limit the fast volatility of the oil and guaranteed a better application and an easier removal from the artefacts attacked by biodeteriogens both indoor and outdoor. This formulation caused the elimination of biodeteriogens from treated surfaces without residuals or films on artworks surface, and the effect was retained up to four months

First principles studies of modulated Co/Cu superlattices with strongly and weakly exchange biased Co-monolayers

First-principles calculations have been performed in order to determine effective exchange integrals between {\it strongly} and {\it weakly} exchange-coupled Co monolayers in certain modulated periodic $CoCu_2/CoCu_n$-type superlattices with three non-equivalent Co planes, which have not yet been studied hitherto. For $3\le n\le 6$ we find that the two non-equivalent exchange integrals have opposite signs, i.e.~the strong coupling is antiferromagnetic and the weak coupling ferromagnetic, and differ for $n\ne 4$ from each other by one order of magnitude. It is shown that the results depend on the system as a whole and could not be obtained from separate parts. Finally we suggest that ''spin valve'' systems of such kind should be considered when trying to obtain good magneto-resistance together with low switching-fields.Comment: LaTex, 9 pages, including two .eps-figure

Ab initio study of mirages and magnetic interactions in quantum corrals

The state of the art ab initio calculations of quantum mirages,the spin-polarization of surface-state electrons and the exchange interaction between magnetic adatoms in Cu and Co corrals on Cu(111) are presented. We find that the spin-polarization of the surface-state electrons caused by magnetic adatoms can be projected to a remote location and can be strongly enhanced in corrals compared to an open surface.Our studies give a clear evidence that quantum corrals could permit to tailor the exchange interaction between magnetic adatoms at large separations. The spin-polarization of surface-state electrons at the empty focus in the Co corral used in the experimental setup of Manoharan et al., (Nature 403, 512 (2000)) is revealed.Comment: Submitted to Physical Review Letter

Oscillatory Thickness Dependence of Magnetic Moments and interface-induced Changes of the Exchange Coupling in Co/Cu and Co-Ni/Cu Multilayers

We perform first-principles calculations for the three multilayer systems (100)-Co_1/Cu_n, -NiCo_2Ni/Cu_n and -Co_4/Cu_n, and find from a comparison x of the results for system 2 and 3 that amplitude and phase of the exchange coupling are sensitive to the magnetic-slab/nonmagnetic-spacer interface. Moreover, we observe that for the system 1 and 2 the averaged magnetic moment of the magnetic slab oscillates with the spacer thickness similarly as the exchange coupling.Comment: 5 pages (Latex, to be applied 2 times) + 2 figures (.ps-files

Multilayer Complex Network Descriptors for Color-Texture Characterization

A new method based on complex networks is proposed for color-texture analysis. The proposal consists on modeling the image as a multilayer complex network where each color channel is a layer, and each pixel (in each color channel) is represented as a network vertex. The network dynamic evolution is accessed using a set of modeling parameters (radii and thresholds), and new characterization techniques are introduced to capt information regarding within and between color channel spatial interaction. An automatic and adaptive approach for threshold selection is also proposed. We conduct classification experiments on 5 well-known datasets: Vistex, Usptex, Outex13, CURet and MBT. Results among various literature methods are compared, including deep convolutional neural networks with pre-trained architectures. The proposed method presented the highest overall performance over the 5 datasets, with 97.7 of mean accuracy against 97.0 achieved by the ResNet convolutional neural network with 50 layers.Comment: 20 pages, 7 figures and 4 table

Theory of interlayer exchange interactions in magnetic multilayers

This paper presents a review of the phenomenon of interlayer exchange coupling in magnetic multilayers. The emphasis is put on a pedagogical presentation of the mechanism of the phenomenon, which has been successfully explained in terms of a spin-dependent quantum confinement effect. The theoretical predictions are discussed in connection with corresponding experimental investigations.Comment: 18 pages, 4 PS figures, LaTeX with IOP package; v2: ref. added. Further (p)reprints available from http://www.mpi-halle.de/~theory