The Crystal Structure of Ba2CuAlF9: a New Structure Type in Copper Fluoride Chemistry

Ba₂CuAlF₉ is monoclinic: a = 5.374(2) Å, b = 7.312(2) Å, c = 9.371(3) Å, β = 90.20(1)°, Z = 2, space group P2₁/c (n° 14). The crystal structure was solved from X-ray single crystal data using 1071 unique reflections (900 with F_o/σ(F_o) > 4, R factor = 0.075). It is built up from infinite isolated cis chains of [MF₆] mixed occupied fluorine octahedra sharing each, one edge and one vertex (M is randomly Cu or Al). An analogous kind of linkage was already observed for two other compounds from the ternary system BaF₂/CuF₂/AlF₃. Close structural relationships exist between the cationic subnetworks of γ-BaAlF₅ and Ba₂CuAlF₉.     

Progressive addition of GO to TiO2 nanowires for remarkable changes in photochemical hydrogen production

Addition of 2D GO to the TiO₂ nanowires brings about progressive changes in the optical properties and photochemical hydrogen production. The composition with progressive addition of GO played a dramatic role in making the material blue shift. The blue shift may happen due to transition from O²⁻ anti-bonding orbital to the Ti⁴⁺ lowest empty orbital and also the process of band shifting towards lower wavelength is attributed to quantum confinement effect which occurs due to the transformation of bulk titanate to nanostructure titanate. In this article, we present the results of TiO₂ nanowires and its rGO composites. TiO₂ with 30 mg rGO nanocomposite exhibits good UV-light induced hydrogen production unlike bare TiO₂. Current studies explain how rGO addition can be employed for better hydrogen production.

     

Hybrid integration for silicon photonics applications

In this paper we show how III-V semiconductors can benefit from advanced silicon fabrication processes and comply with their environment in particular to achieve electrically pumped III-V on silicon lasers for both intra-chip and off-chip applications.     

Imidazolium Salt Ion Pairs in Solution

The formation, stabilisation and reactivity of contact ion pairs of non‐protic imidazolium ionic liquids (ILs) in solution are conceptualized in light of selected experimental evidence as well theoretical calculations reported mainly in the last ten years. Electric conductivity, NMR, ESI‐MS and IR data as well as theoretical calculations support not only the formation of contact ion pairs in solution, but also the presence of larger ionic and neutral aggregates even when dissolved in solvents with relatively high dielectric constants, such as acetonitrile and DMSO. The presence of larger imidazolium supramolecular aggregates is favoured at higher salt concentrations in solvents of low dielectric constant for ILs that contain shorter N‐alkyl side chains associated with anions of low coordination ability. The stability and reactivity of neutral contact species are also dependent on the nature of the anion, imidazolium substituents, and are more abundant in ILs containing strong coordinating anions, in particular those that can form charge transfer complexes with the imidazolium cation. Finally, some ILs display reactivities as contact ion pairs rather than solvent‐separated ions.     

Caldero–Keller Approach to the Denominators of Cluster Variables

Buan, Marsh, and Reiten proved that if a cluster-tilting object T in a cluster category 𝒞 associated to an acyclic quiver Q satisfies certain conditions with respect to the exchange pairs in 𝒞, then the denominator in its reduced form of every cluster variable in the cluster algebra associated to Q has exponents given by the dimension vector of the corresponding module over the endomorphism algebra of T. In this article, we give an alternative proof of this result using the Caldero–Keller approach to acyclic cluster algebras and the work of Palu on cluster characters.     

Formule de Pesin et applications méromorphes

Résumé. Soit f une application méromorphe dominante définie sur une variété compacte k?hlérienne X et μ une mesure invariante ergodique dont les exposants de Lyapounov sont strictement positifs. On suppose que les fonctions quasiplurisousharmoniques sont μ-intégrables. Nous montrons que μ est absolument continue par rapport à la mesure volume si μ satisfait la formule de Pesin.      

Law-of-the-wall in a boundary-layer over regularly distributed roughness elements

As opposed to the log-region, the roughness sublayer present above rough surfaces is still poorly understood due to the complex interaction between wakes developing behind roughness elements. To investigate the spatially averaged flow velocity in this region, a data-set has been collected from several direct numerical simulations and wind-tunnel experiments available in the literature. A generalised law-of-the-wall has been derived, applicable to a roughness sublayer present over regularly distributed roughness elements. The key roughness parameter of this new law is the effective height ?, which characterises the interaction between the roughness and the outer flow in a temporally and spatially averaged sense. A morphometric study reveals that ? is closely related to a new roughness density parameter, λ₂, that accounts for the roughness element shape and the inter-element spacing. This allows ? to be a universal parameter on roughness characterisation. The derived values of the classical roughness length z₀ of the log-law compare well with previous experimental data and geometrical model predictions. Finally, the main properties of the roughness sublayer such as its height are discussed using the geometrical and the roughness parameters proposed in the study.     

Sound absorption properties of a sunflower composite made from crushed stem particles and from chitosan bio-binder

A recent study investigated the mechanical, thermal and acoustical properties of a bio-based composite made from crushed particles of sunflower stalks binded together by chitosan, a bio-based binder. The acoustical performance in absorption was found to be poor as the material was highly compacted and with low porosity. The present study focuses on the acoustical properties of a higher porosity composite, with lower density while the mechanical rigidity remains fairly high. A higher absorption coefficient is obtained. The experimental results on the absorption coefficient are compared to the prediction of a model involving 5 physical parameters (porosity, tortuosity, airflow resistivity, thermal and viscous characteristic lengths). The characterization methods to determine these parameters are described. The comparison between experimental and theoretical results shows that this material exhibits peculiar microstructural features. It is found that the sound absorption properties can involve dead-end pores or clusters and multiple porosity scales in the material.