Minimum weight limit design under uncertainty

Summary The problem of probabilistic minimum weight limit design is formulated as a stochastic programming problem. The theoretical treatment considers monodimensional structures, geometrical parameters and integer design variables. An algorithm is proposed and illustrated for the case of pin-jointed structures with two random continuous variables. The paper follows previous researches of the Authors in the field of probabilistic approach to structural safety [29 ÷ 33].

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Sommario Il problema della progettazione a rottura per minimo peso su basi probabilistiche viene formulato quale problema di programmazione stocastica. La trattazione teorica si estende alle strutture monodimensionali, comprende variabili di tipo geometrico nonchè variabili intere: l'algoritmo proposto ed illustrato per la risoluzione numerica riguarda le strutture reticolari interessate da due variabili casuali continue. Il lavoro fa seguito a precedenti ricerche degli scriventi in tema di concezione probabilistica della sicurezza [29 ÷ 33].

     

Synthesis and Characterization of an Unusual 68-Electrons Os4Se3 Carbonyl Phosphane Cluster

The 68-electrons, phosphane-substituted, osmium selenido-carbonyl cluster [Os₄Se₃(CO)₁₀(dppm)] (cluster 3; dppm = bis(diphenylphosphino)methane) has been obtained by reaction under mild experimental conditions between [Os₃(CO)₁₂] and the diphosphane diselenide dppmSe₂. Its crystal and molecular structure has been elucidated by X-ray diffraction methods. Cluster 3 contains only two Os–Os bonds as suggested by its electron count. It can be described as derived from the open-triangular nido cluster [Os₃(μ₃-Se)₂(CO)₉] through substitution of one CO ligand by the four-electrons donor osmiaselone fragment [CH₂(Ph₂P)₂](CO)₂Os=Se. The replacement of a two-electrons donor carbonyl with a four-electron donor fragment produces the cleavage of one Os–Os bond in the nido cluster. Under the adopted experimental conditions, other products of the reaction between [Os₃(CO)₁₂] and dppmSe₂ are the clusters [Os₃(μ₃-Se)₂(CO)₉] (1), [Os₃(μ₃-Se)₂(CO)₇(μ-dppm)] (2), and [Os₃(μ₃-Se)(CO)₈(μ-dppm)] (4), already described in the literature.     

A Detailed Study of the (Electro)chemical Behavior of Bis(trifluoromethanesulfonyl)imide Based Ionic Liquids at Different Purification Steps

A systematic investigation of the major impurities content as well as of their effect on the electrochemical behavior of synthesized N‐butyl‐N‐methylpyrrolidinium (Py_1.4), N‐(2‐methoxyethyl)‐N‐methylpyrrolidinium (Py_1.102) and 1‐butyl‐3‐methylimidazolium (bmim) bis(trifluoromethanesulfonyl)imide has been carried out and the efficacy of an optimized multistep purification protocol for obtaining ILs suitable for electrochemical applications has been verified.     

The Structure of Sub‐nm Platinum Clusters at Elevated Temperatures

Little is known about metallic clusters consisting merely of a dozen of atoms or even less, despite of their importance in catalysis and crystal nucleation. Scanning transmission electron microscopy (STEM) provides direct atomic structure information but has inherently suffered from limited time resolution. We employ fast dynamic STEM combined with a spatio‐temporal image denoising algorithm to explore the structure and stability of Pt clusters on carbon, which represents a highly relevant catalysis system. At room temperature, dynamic amorphous 2D structures are found, while above ≈300 °C, the clusters transform into a crystalline state. Our experimental and theoretical data reveal an unexpected strong trend of the crystalline clusters to exhibit the face‐centered cubic, bulk structure of Pt with cuboidal geometries being most prominent.     

Surface Modification with Control over Ligand Density for the Study of Multivalent Biological Systems

In the study of multivalent interactions at interfaces, as occur for example at cell membranes, the density of the ligands or receptors displayed at the interface plays a pivotal role, affecting both the overall binding affinities and the valencies involved in the interactions. In order to control the ligand density at the interface, several approaches have been developed, and they concern the functionalization of a wide range of materials. Here, different methods employed in the modification of surfaces with controlled densities of ligands are being reviewed. Examples of such methods encompass the formation of self-assembled monolayers (SAMs), supported lipid bilayers (SLBs) and polymeric layers on surfaces. Particular emphasis is given to the methods employed in the study of different types of multivalent biological interactions occurring at the functionalized surfaces and their working principles.     

Comparison of Different Sorbents in the QuEChERS Method for the Determination of Pesticide Residues in Strawberries by LC–MS/MS

A comparison of sample preparation based on the quick, easy, cheap, effective, rugged and safe (QuEChERS) method for analysis of pesticide residues in strawberries by LC–MS/MS was made using different sorbents in the clean-up by dispersive solid-phase extraction (d-SPE). Some sorbents were laboratory-made, prepared by depositing poly(methyloctadecylsiloxane) (PMODS), poly(methyloctylsiloxane) (PMOS), aminopropyl-terminated poly(dimethylsiloxane) (APPS) and copolymer of (52–48 %)dimethyl-(48–52 %)methylphenyl-siloxane (DMMPS) onto silica supports. The commercial sorbent primary–secondary amine (PSA) and mixtures of two sorbents, primary–secondary amine and poly(methyloctadecylsiloxane), were also used in the experiments. The performances of the sorbents were evaluated by parameters such as color of the final extract, gravimetric measurement, recovery and matrix effect at the fortification level of 100 ng g^?1 of the pesticide mixture in strawberries. The recoveries were in the range 70–120 %, and the RSD values were lower than 20 % for most of the pesticides using the modified QuEChERS method with different sorbents in the clean-up step. The strawberry extracts were cleaned more efficiently with the use of primary–secondary amine sorbent, which has the function of removing sugars, organic acids and especially pigments. The sample preparation method was efficient, and LC–MS/MS determination was optimal because of high selectivity and good detectivity for the multiresidue analyses.     

Benchmarking dispersion and geometrical counterpoise corrections for cost‐effective large‐scale DFT calculations of water adsorption on graphene

The physisorption of water on graphene is investigated with the hybrid density functional theory (DFT)‐functional B3LYP combined with empirical corrections, using moderate‐sized basis sets such as 6‐31G(d). This setup allows to model the interaction of water with graphene going beyond the quality of classical or semiclassical simulations, while still keeping the computational costs under control. Good agreement with respect to Coupled Cluster with singles and doubles excitations and perturbative triples (CCSD(T)) results is achieved for the adsorption of a single water molecule in a benchmark with two DFT‐functionals (Perdew/Burke/Ernzerhof (PBE), B3LYP) and Grimme's empirical dispersion and counterpoise corrections. We apply the same setting to graphene supported by epitaxial hexagonal boron nitride (h‐BN), leading to an increased interaction energy. To further demonstrate the achievement of the empirical corrections, we model, entirely from first principles, the electronic properties of graphene and graphene supported by h‐BN covered with different amounts of water (one, 10 water molecules per cell and full coverage). The effect of h‐BN on these properties turns out to be negligibly small, making it a good candidate for a substrate to grow graphene on. © 2014 Wiley Periodicals, Inc.     

Photochemical synthesis of perfluoropolyether (PFPE) nanocomposites containing PFPE oligomer stabilized magnetite nanoparticles

Magnetite nanoparticles were synthesized and their post-synthesis surface modification was carried out with triethoxy terminated perfluoropolyether (PFPE) oligomers. The surface-treated nanoparticles were then dispersed in a UV-curable difunctional methacrylic PFPE oligomer. Thin films prepared from the resulting stable suspensions were photopolymerized. The obtained nanocomposites showed good distribution of the surface-treated magnetite nanoparticles in the polymer matrix. The surface treatment of magnetite nanoparticles with perfluoropolyether oligomers thus was found to be effective in preventing nanoparticle segregation and aggregation, ensuring therefore an increased compatibility with the PFPE matrix.