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We explore, both experimentally and theoretically, the existence in the millimeter-wave range of the phenomenon of extraordinary light transmission through arrays of subwavelength holes. We have measured the transmission spectra of several samples made on aluminum wafers by use of an AB Millimetre quasi-optical vector network analyzer in the wavelength range 4.2-6.5 mm. Clear signals of the existence of resonant light transmission at wavelengths close to the period of the array appear in the spectra.

This work explores from a theoretical viewpoint the mechanical properties of the most important hydration product present in cementitious environments, the so called C‐S‐H (calcium‐silicate‐hydrate) gel. The dependence of the bulk (K), shear (G) and Young's (E) modulus for the C‐S‐H crystals respect to its composition and the length of its silicate chains is analysed by lattice dynamic simulations with parameterised two‐body and three‐body potentials. Our simulations reveal that the mechanical properties of C‐S‐H crystals show a strong dependence on their composition. Nevertheless our calculated numbers systematically overestimate the experimental values for C‐S‐H gels. Only when the finite length of the silicate chains is taken into account this discrepancy disappears. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In this article, we study the polymerization of silicic acids (Si(OH)4) in the presence of calcium ions by molecular dynamics simulations. We focus on the formation and structure of cementitious calcium silicate hydrate (C–S–H) gels. Our simulations confirm that, in accordance with experiments, a larger content of calcium ions slows down the polymerization of the cementitious silicate chains and prevents them from forming rings and three‐dimensional structures. Furthermore, by an analysis of the connectivity of our simulated silicate chains and by a count of the number of Ca–OH and Si–OH bonds formed, the relationship with commonly used structural models of C–S–H gels, such as 1.4 nm tobermorite and jennite, is discussed.

The NMR spectra of 29 Si in cement-based materials are studied through calculations of the isotropic shielding of silicon atoms within the density functional theory. We focus on the main component of cement, the calcium-silicate-hydrate gel, using widely accepted models based on the observed structures of jennite and tobermorite minerals. The results show that the 29 Si chemical shifts are dependent not only on the degree of condensation of the (SiO 4 ) units, as commonly assumed, but also on the local arrangement of the charge compensating H and Ca cations. We find that the NMR spectra for models of the calcium-silicate-hydrate gel based on tobermorite are in better agreement with experiment than those for jennite-based models.Article pubs.acs.org/JPCC

The delicate interplay between plasmonic excitations and interband transitions in noble metals is described by means of {\it ab initio} calculations and a simple model in which the conduction electron plasmon is coupled to the continuum of electron-hole pairs. Band structure effects, specially the energy at which the excitation of the $d$-like bands takes place, determine the existence of a subthreshold plasmonic mode, which manifests itself in Ag as a sharp resonance at 3.8 eV. However, such a resonance is not observed in the other noble metals. Here, this different behavior is also analyzed and an explanation is provided.Comment: 9 pages, 8 figure