Synthesis,Crystal Structure and Optical Properties of LaNbON2

LaNbON₂ was synthesized by thermal ammonolysis of crystalline LaNbO₄ prepared by a soft chemistry approach. LaNbON₂ crystallizes in a distorted GdFeO₃‐like perovskite structure with space group Pnma and a = 5.5720(2), b = 7.8656(4), c = 5.6066(3) Å and a random anionic arrangement as revealed by neutron diffraction. Elongated displacement ellipsoids found by neutron diffraction and a considerable degree of residual bond strain as revealed by the bond valence calculations suggest a local positional disorder of the niobium ions.The material exhibits good chemical stability at ambient conditions and a considerable thermal stability upon heating in synthetic air (up to T = 500 K) as well as a small optical band gap of ~1.7 eV.     

Chaos,border collisions and stylized empirical facts in an asset pricing model with heterogeneous agents

Nonlinear Dynamics - An asset pricing model with chartists, fundamentalists and trend followers is considered. A market maker adjusts the asset price in the direction of the excess demand at the...     

Finite Dimensional Global Attractor for 3D MHD-α Models: A Comparison

We consider two magnetohydrodynamic-α (MHDα) models with kinematic viscosity and magnetic diffusivity for an incompressible fluid in a three-dimensional periodic box (torus). More precisely, we consider the Navier–Stokes-α-MHD and the Modified Leray-α-MHD models. Similar models are useful to study the turbulent behavior of fluids in presence of a magnetic field because of the current impossibility to handle non-regularized systems neither analytically nor via numerical simulations. In both cases, the global existence of the solution and of a global attractor can be shown. We provide an upper bound for the Hausdorff and the fractal dimension of the attractor. This bound can be interpreted in terms of degrees of freedom of the long-time dynamics of the involved system and gives information about the numerical stability of the model. We get the same bound that holds for the Simplified Bardina-MHD model, considered in a previous paper (this result provides, in some sense, an intermediate bound between the number of degrees of freedom for the Simplified Bardina model and the Navier–Stokes-α equation in the nonmagnetic case). However, the Navier–Stokes-α-MHD system is preferable since, in the ideal case, it conserves more quadratic invariants derived from the standard MHD model.     

Mechanical Properties of the Nanometer Scale Precrystalline Order of a Poly(ethylene terephthalate)/Poly(ethylene naphthalate) Blend

Summary: Nanometer scale morphological order of macroscopically amorphous polyesters, obtained from the melt at moderate cooling rates, was observed in the past. The effect of such order on mechanical properties of a PET/PEN blend, evaluated by AFM nanoindentations, is reported in this study. Results show that nanoindentations conducted at relatively high load, with penetration depths of the order of 100 nm, confirm the information obtained from mechanical tests at micrometer scale, i.e., microhardness. On the other hand, true nanometer scale indentations (<40 nm) are seen to discriminate between the mechanical properties of the nanophases formed during solidification.

Statistical distribution of elastic moduli observed after 60 nanoindentations performed at 1 µN on each sample solidified at the cooling rates reported in the legend.     

A Model Assessment of the Occurrence and Reactivity of the Nitrating/Nitrosating Agent Nitrogen Dioxide (•NO2) in Sunlit Natural Waters

Nitrogen dioxide (^•NO₂) is produced in sunlit natural surface waters by the direct photolysis of nitrate, together with ^•OH, and upon the oxidation of nitrite by ^•OH itself. ^•NO₂ is mainly scavenged by dissolved organic matter, and here, it is shown that ^•NO₂ levels in sunlit surface waters are enhanced by high concentrations of nitrate and nitrite, and depressed by high values of the dissolved organic carbon. The dimer of nitrogen dioxide (N₂O₄) is also formed in the pathway of ^•NO₂ hydrolysis, but with a very low concentration, i.e., several orders of magnitude below ^•NO₂, and even below ^•OH. Therefore, at most, N₂O₄ would only be involved in the transformation (nitration/nitrosation) of electron-poor compounds, which would not react with ^•NO₂. Although it is known that nitrite oxidation by CO₃^•− in high-alkalinity surface waters gives a minor-to-negligible contribution to ^•NO₂ formation, it is shown here that NO₂⁻ oxidation by Br₂^•− can be a significant source of ^•NO₂ in saline waters (saltwater, brackish waters, seawater, and brines), which offsets the scavenging of ^•OH by bromide. As an example, the anti-oxidant tripeptide glutathione undergoes nitrosation by ^•NO₂ preferentially in saltwater, thanks to the inhibition of the degradation of glutathione itself by ^•OH, which is scavenged by bromide in saltwater. The enhancement of ^•NO₂ reactions in saltwater could explain the literature findings, that several phenolic nitroderivatives are formed in shallow (i.e., thoroughly sunlit) and brackish lagoons in the Rhône river delta (S. France), and that the laboratory irradiation of phenol-spiked seawater yields nitrophenols in a significant amount.     

Static condensation method for the reduced dynamic modeling of mechanisms and structures

Archive of Applied Mechanics - In this paper, a novel static condensation method is extended to mechanisms and structures with internal joints. The formulation is framed inside the static reduction...     

Design of Single Gold Atoms on Nitrogen‐Doped Carbon for Molecular Recognition in Alkyne Semi‐Hydrogenation

Single‐atom heterogeneous catalysts with well‐defined architectures are promising for deriving structure–performance relationships, but the challenge lies in finely tuning the structural and electronic properties of the metal. To tackle this point, a new approach based on the surface diffusion of gold atoms on different cavities of N‐doped carbon is presented. By controlling the activation temperature, the coordination neighbors (Cl, O, N) and the oxidation state of the metal can be tailored. Semi‐hydrogenation of various alkynes on the single‐atom gold catalysts displays substrate‐dependent catalytic responses; structure insensitive for alkynols with γ‐OH and unfunctionalized alkynes, and sensitive for alkynols with α‐OH. Density functional theory links the sensitivity for alkynols to the strong interaction between the substrate and specific gold‐cavity ensembles, mimicking a molecular recognition pattern that allows to identify the cavity site and to enhance the catalytic activity.     

A periodic review policy for a coordinated single vendor-multiple buyers supply chain with controllable lead time and distribution-free approach

4OR - In this paper, we study a single vendor-multiple buyer integrated inventory model with controllable lead time and backorders-lost sales mixture. Each buyer adopts a periodic review policy in...     

Approximation of eigenvalues of evolution operators for linear coupled renewal and retarded functional differential equations

Ricerche di Matematica - Recently, systems of coupled renewal and retarded functional differential equations have begun to play a central role in complex and realistic models of population...     

A simply tunable electromagnetic pendulum energy harvester

Meccanica - A fundamental issue for the advance of self-sustainable electronic systems and remote sensor is the development of energy harvesters able to efficiently convert ambient energy into...