Shell-anchor-core structures for enhanced stability and catalytic oxygen reduction activity

Density functional theory is used to evaluate activity and stability properties of shell-anchor-core structures. The structures consist of a Pt surface monolayer and a composite core having an anchor bilayer where C atoms in the interstitial sites lock 3d metals in their locations, thus avoiding their surface segregation and posterior dissolution. The modified subsurface geometry induces less strain on the top surface, thus exerting a favorable effect on the surface catalytic activity where the adsorption strength of the oxygenated species becomes more moderate: weaker than on pure Pt(111) but stronger than on a Pt monolayer having a 3d metal subsurface. Here we analyze the effect of changing the nature of the 3d metal in the subsurface anchor bilayer, and we also test the use of a Pd monolayer instead of Pt on the surface. It is found that a subsurface constituted by two layers with an approximate composition of M(2)C (M = Fe, Ni, and Co) provides a barrier for the migration of subsurface core metal atoms to the surface. Consequently, an enhanced resistance against dissolution in parallel to improved oxygen reduction activity is expected, as given by the values of adsorption energies of reaction intermediates, delayed onset of water oxidation, and/or low coverage of oxygenated species at surface oxidation potentials.     

Preparation and Flame Retardancy Properties of Novel PA12 and PE/Layered Titanoniobates Nanocomposites

Summary: We report herein a study performed on a layered titanoniobate KTiNbO₅ modified by octadecylamine to evaluate the fire retardancy properties of this novel hybrid nanofiller dispersed in PA12 and LLDPE, by polymer melt intercalation. The nanocomposites have been characterized using Electron Microscopy techniques to evaluate the degree of exfoliation and the morphologies. Thermogravimetric analyses and cone calorimeter tests have been carried out to assess the fire retardant performances.     

Polypropylene Nanocomposites,Study of the Influence of the Nanofiller Nature on Morphology and Material Properties

Summary: In this paper we investigate the influence of various nanofilllers' aspect ratio, chemical nature and organic modification on some selected polypropylene properties, such as crystallinity, thermal and mechanical resistance and fire behaviour. Materials were prepared by twin-screw extrusion and characterized by means of scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, tensile and cone calorimeter tests. Fillers characteristics were found to influence at different extents, and for different reasons, the material final properties.     

On the 3-restricted edge connectivity of permutation graphs

An edge cut W of a connected graph G is a k-restricted edge cut if G−W is disconnected, and every component of G−W has at least k vertices. The k-restricted edge connectivity is defined as the minimum cardinality over all k-restricted edge cuts. A permutation graph is obtained by taking two disjoint copies of a graph and adding a perfect matching between the two copies. The k-restricted edge connectivity of a permutation graph is upper bounded by the so-called minimum k-edge degree. In this paper some sufficient conditions guaranteeing optimal k-restricted edge connectivity and super k-restricted edge connectivity for permutation graphs are presented for k=2,3.     

Theoretical study on the properties of linear and cyclic amides in gas phase and water solution

The structural and energetic properties of a group of selected amides, of well-known importance for the design of efficient clathrate inhibitors, are calculated with Hartree-Fock and density functional theory, B3LYP, theoretical levels, and a 6-311++g** basis set in the gas phase and a water solution. The conformational behavior of the molecules is studied through the scanning of the torsional potential energy surfaces and by the analysis of the differences in the energetic and structural properties between the isomers. The properties of the amides in water solution are determined within a self-consistent reaction field approach with a polarizable continuum model that allows the calculation of the different contributions to the free energy of solvation. The calculated barriers to rotation are in good agreement with the available experimental data and the comparison of the gas and water results shows the strong effect of the solute polarization. The properties of different amide-water complexes are calculated and compared with available experimental information.     

Local search and genetic algorithm for the job shop scheduling problem with sequence dependent setup times

The Job Shop Scheduling Problem (JSP) is an example of a combinatorial optimization problem that has interested researchers for several decades. In this paper we confront an extension of this problem called JSP with Sequence Dependent Setup Times (SDST-JSP). The approach extends a genetic algorithm and a local search method that demonstrated to be efficient in solving the JSP. For local search, we have formalized neighborhood structures that generalize three well-know structures defined for the JSP. We have conducted an experimental study across conventional benchmark instances showing that the genetic algorithm exploited in combination with the local search, considering all three neighborhoods at the same time, provides the best results. Moreover, this approach outperforms the current state-of-the-art methods.     

Uniqueness of unconditional basis in quasi-Banach spaces which are not sufficiently Euclidean

Strongly absolute bases are, roughly speaking, purely nonlocally convex bases in quasi-Banach spaces. When, in addition, they are unconditional then the discrete lattice structure they induce in the space is lattice anti-Euclidean. In this brief note we characterize the complemented unconditional basic sequences in those quasi-Banach spaces with strongly absolute unconditional basis, and use this result to derive the uniqueness of unconditional basis in many classical quasi-Banach spaces.     

On the restricted arc-connectivity of s-geodetic digraphs

For a strongly connected digraph D the minimum ,cardinality of an arc-cut over all arc-cuts restricted arc-connectivity λ′（D） is defined as the S satisfying that D - S has a non-trivial strong component D1 such that D - V（D1） contains an arc. Let S be a subset of vertices of D. We denote by w＋（S） the set of arcs uv with u ∈ S and v S, and by w-（S） the set of arcs uv with u S and v ∈ S. A digraph D = （V, A） is said to be λ′-optimal if λ′（D） =ξ′（D）, where ξ′（D） is the minimum arc-degree of D defined as ξ（D） = min {ξ′（xy） ： xy ∈ A}, and ξ′（xy） = min（｜ω＋（{x,y}）｜, ｜w-（{x,y}）｜, ｜w＋（x） ∪ w- （y） ｜, ｜w- （x） ∪ω＋ （y）｜}. In this paper a sufficient condition for a s-geodetic strongly connected digraph D to be λ′-optimal is given in terms of its diameter. Furthermore we see that the h-iterated line digraph Lh（D） of a s-geodetic digraph is λ′-optimal for certain iteration h.     

On the connectivity and superconnected graphs with small diameter

In this paper, first we prove that any graph G is 2-connected if diam(G)≤g−1 for even girth g, and for odd girth g and maximum degree Δ≤2δ−1 where δ is the minimum degree. Moreover, we prove that any graph G of diameter diam(G)≤g−2 satisfies that (i) G is 5-connected for even girth g and Δ≤2δ−5, and (ii) G is super-κ for odd girth g and Δ≤3δ/2−1.     

Nylon‐6 nanocomposites,study of the influence of the nanofiller nature on morphology and material properties

In this article we investigated the influence of various nanofilllers' aspect ratio, chemical nature, and organic modification on some selected nylon‐6 properties, such as crystallinity, thermal and mechanical resistance, and fire behavior. Materials were prepared by twin‐screw extrusion and characterized by means of scanning and transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, tensile tests, and cone calorimeter. Fillers characteristics were found to influence at different extents the material final properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1935–1948, 2009