Omnidirectional bandgap in Cantor dielectric multilayers

Analysis of the transmission spectrum of Cantor dielectric multilayers for obliquely incident plane wave shows that the main bandgap shifts towards higher frequencies, substantially retaining its shape, as the incidence angle increases for both s- and p-polarization of the impinging wave. For suitable refractive index values of the two constituent materials a range of frequencies can be found where transmission of the incident wave is almost completely forbidden at any angle of incidence. This omnidirectional bandgap can be found also for lossy media. In this case the stop-band widens as the tangent loss increases, while the depth of the stop-band does not change significantly. Comparison with the periodic quarter-wave stack shows that the Cantor multilayer exhibits a narrower omnidirectional bandgap with transmissivity values that are about one order of magnitude lower.     

Solute Transport Analysis Through Heterogeneous Media in Nonuniform in the Average Flow by a Stochastic Approach

The stochastic approach has been shown to be an excellent tool for the characterisation and analysis of velocity fields and transport processes through heterogeneous porous formations. The main results (linear theory) have been obtained for problems with simplified flow conditions, usually in the assumption of uniform in the average flow, but a great effort is spent to reach theoretical results for more complex situations.This paper deals with 2D heterogeneous aquifers subject to uniform recharge; the stochastic approach is adopted to characterise, as ensemble behaviour, the velocity field and transport processes of a nonreactive solute. The impact of transmissivity conditioning on solute particles trajectories is analysed and an application is carried out. The analytical formulations, obtained by a first order analysis, are compared to the one resulting from constant in the average hydraulic gradient, and their reliability is investigated with numerical tests performed by a Monte Carlo method.The result of this study is that strong non-stationarities are present in the flow and transport process. A detailed analysis shows that the theoretical results cannot be extended to cases with high heterogeneity level, unlike the uniform in the average flow fields.     

Selective oxidation of sulfides to sulfoxides and sulfones using 30% aqueous hydrogen peroxide and silica-vanadia catalyst

A green, efficient and selective approach for the oxidation of sulfides to sulfoxides and sulfones with stoichiometric amount of 30% aq. H₂O₂ is reported. The reaction is performed in methanol with silica-vanadia as heterogeneous and reusable catalyst.     

Alkyd paints in art: Characterization using integrated mass spectrometry

Alkyd resins have been commonly used as binders in artist paints since the 1940s. The characterization of alkyds in samples from artworks can help to solve attribution and dating issues, investigate decay processes, and contribute to the planning of conservation strategies. Being able to assess the components of industrially formulated paint materials and to differentiate between different trademarks and producers is extremely interesting and requires multi-analytical approaches.     

Minimal full polarized embeddings of dual polar spaces

Let Δ be a thick dual polar space of rank n ≥ 2 admitting a full polarized embedding e in a finite-dimensional projective space Σ, i.e., for every point x of Δ, e maps the set of points of Δ at non-maximal distance from x into a hyperplane e∗(x) of Σ. Using a result of Kasikova and Shult [11], we are able the show that there exists up to isomorphisms a unique full polarized embedding of Δ of minimal dimension. We also show that e∗ realizes a full polarized embedding of Δ into a subspace of the dual of Σ, and that e∗ is isomorphic to the minimal full polarized embedding of Δ. In the final section, we will determine the minimal full polarized embeddings of the finite dual polar spaces DQ(2n,q), DQ ⁻(2n+1,q), DH(2n−1,q ²) and DW(2n−1,q) (q odd), but the latter only for n≤ 5. We shall prove that the minimal full polarized embeddings of DQ(2n,q), DQ ⁻(2n+1,q) and DH(2n−1,q ²) are the `natural' ones, whereas this is not always the case for DW(2n−1, q).B. De Bruyn: Postdoctoral Fellow of the Research Foundation - Flanders.     

On a long-standing conjecture by Pólya–Szegö and related topics

The electrostatic capacity of a convex body is usually not simple to compute. We discuss two possible approximations of it. The first one is related to a long-standing conjecture by Pólya–Szegö. It states that, among all convex bodies, the “worst shape” for the approximation exists and is the planar disk. We prove the first part of this conjecture, and we establish some related results which give further evidence for the validity of the second part. We also suggest some complementary conjectures and open problems. The second approximation we study is based on the use of web functions.Received: September 29, 2003     

Mass spectrometric characterization of metal triflates and triflimides (Lewis superacid catalysts) by electrospray ionization and tandem mass spectrometry

Trifluoromethylsulfonate (triflate) and bis(trifluoromethylsulfonyl)imide (triflimide) salts, well‐known Lewis acid catalysts, present some difficulty in their characterization. By using nitromethane as the solvent, useful electrospray mass spectra in positive and negative ion mode were obtained for salts of metals in oxidation states +2 and +3. In positive mode, addition of a strong Lewis base (triphenylphosphine oxide, TPPO), capable of displacing a triflate (TfO^?) or a triflimide (Tf₂N^?) anion, is necessary for obtaining useful spectra. Under these conditions of solvent and added ligand, the most abundant ions were [M²⁺(A^?)(TPPO)₂]⁺ or [M³⁺(A^?)₂(TPPO)₂]⁺ with A^? = TfO^? or Tf₂N^?. The MS/MS spectra of these diagnostic ions provide additional analytical information. The breakdown curves, in the form of % dissociated as a function of the ion activation energy, offer a mean for investigating the bonding in these ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Multicomponent synthesis of dihydrobenzoxazepinones,bearing four diversity points,as potential <Emphasis Type="Italic">α</Emphasis>-helix mimics

A very short convergent synthesis of dihydrobenzoxazepinones, bearing four diverse diversity points, based on coupling the Ugi reaction with a Mitsunobu cyclization, was developed. These compounds are potential α-helix mimics, where three of the four appendages are expected to imitate the residues in i, i + 4 and i + 7 positions. A library of 22 compounds bearing lipophilic substituents, designed to interact with the hydrophobic cleft of anti-apoptotic protein Bcl-xL, was synthesized. Preliminary biochemical tests, based on competitive binding, have already been carried out.     

Recent advances in analytical and bioanalysis applications of noble metal nanorods

In the last decade the use of anisotropic nanoparticles in analytical and bioanalytical applications has increased substantially. In particular, noble metal nanorods have unique optical properties that have attracted the interest of many research groups. The localized surface plasmon resonance (LSPR) generated by interaction of light at a specific wavelength with noble metal nanoparticles was found to depend on particle size and shape and on the constituting material and the surrounding dielectric solution. Because of their anisotropic shape, nanorods are characterized by two LSPR peaks: the transverse, fixed at approximately 530 nm, and the longitudinal, which is in the visible–near infra-red region of the spectrum and varies with nanorod aspect ratio. The intense surface plasmon band enables nanorods to absorb and scatter light in the visible and near infra-red regions, and fluorescence and two-photon induced luminescence are also observed. These optical properties, with the reactivity towards binding events that induce changes in the refractive index of the surrounding solution, make nanorods a useful tool for tracking binding events in different applications, for example assembly, biosensing, in-vivo targeting and imaging, and single-molecule detection by surface-enhanced Raman spectroscopy. This review presents the promising strategies proposed for functionalizing gold nanorods and their successful use in a variety of analytical and biomedical applications.     

Some estimates for the torsional rigidity of composite rods

A well‐known problem in elasticity consists in placing two linearly elastic materials (of different shear moduli) in a given plane domain Ω, so as to maximize the torsional rigidity of the resulting rod; moreover, the proportion of these materials is prescribed. Such a problem may not have a classical solution as the optimal design may contain homogenization regions, where the two materials are mixed in a microscopic scale. Then, the optimal torsional rigidity becomes difficult to compute. In this paper we give some different theoretical upper and lower bounds for the optimal torsional rigidity, and we compare them on some significant domains. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)