Original Preparation of PEKK Dispersion for Coating by Transfer from a Chloroform Stable Dispersion to an Aqueous Stable Dispersion,by Emulsion/Solvent Evaporation

In this work, aqueous dispersions of PolyEtherKetoneKetone (PEKK) oligomers were obtained by an emulsion/dispersion solvent evaporation technique. The PEKK oligomers were synthesized by a Friedel–Crafts acylation with a number average degree of polymerization of 4. The synthesized PEKK oligomers had very good thermal stability and spontaneously formed a stable dispersion of swollen micrometric fibers in chloroform. After sonication of the chloroform dispersion in water in the presence of sodium dodecyl sulfate (SDS) and evaporation, we obtained aggregated particles with a mean diameter between 120 and 160 nm, decreasing linearly with the PEKK concentration. The most stable dispersions were obtained with 0.5% wt of surfactant and, at a fixed concentration of SDS, the stability decreased when the PEKK concentration was increased. The different dispersions of PEKK in water were very stable and, after water evaporation, formed homogeneous films for high-performance coating.     

An assessment of a days off decomposition approach to personnel shift scheduling

This paper studies a two-phase decomposition approach to solving the personnel scheduling problem. The first phase creates a days-off-schedule, indicating working days and days off for each employee. The second phase assigns shifts to the working days in the days-off-schedule. This decomposition is motivated by the fact that personnel scheduling constraints are often divided into two categories: one specifies constraints on working days and days off, while the other specifies constraints on shift assignments. To assess the consequences of the decomposition approach, we apply it to public benchmark instances, and compare this to solving the personnel scheduling problem directly. In all steps we use mathematical programming. We also study the extension that includes night shifts in the first phase of the decomposition. We present a detailed results analysis, and analyze the effect of various instance parameters on the decompositions’ results. In general, we observe that the decompositions significantly reduce the computation time, but the quality, though often good, depends strongly on the instance at hand. Our analysis identifies which aspects in the instance can jeopardize the quality.     

A Generating Tree Approach to <Emphasis Type="Italic">k</Emphasis>-Nonnesting Partitions and Permutations

We describe a generating tree approach to the enumeration and exhaustive generation of k-nonnesting set partitions and permutations. Unlike previous work in the literature which uses the connections of these objects to Young tableaux and restricted lattice walks, our approach deals directly with partition and permutation diagrams. We provide explicit functional equations for the generating functions, with k as a parameter. Key to the solution is a superset of diagrams that permit semi-arcs. Many of the resulting counting sequences also count other well-known objects, such as Baxter permutations, and Young tableaux of bounded height.     

Bottom-up Synthesis of Water-Soluble Gold Nanoparticles Stabilized by N-Heterocyclic Carbenes: From Structural Characterization to Applications

N-heterocyclic carbenes (NHCs) have become attractive ligands for functionalizing gold nanoparticle surfaces with applications ranging from catalysis to biomedicine. Despite their great potential, NHC stabilized gold colloids (NHC@AuNPs) are still scarcely explored and further efforts should be conducted to improve their design and functionalization. Here, the ‘bottom-up’ synthesis of two water-soluble gold nanoparticles ( AuNP-1 and AuNP-2 ) stabilized by hydrophilic mono- and bidentate NHC ligands is reported together with their characterization by various spectroscopic and analytical methods. The NPs showed key differences likely to be due to the selected NHC ligand systems. Transmission electron microscopy (TEM) images showed small quasi-spherical and faceted NHC@AuNPs of similar particle size (ca. 2.3–2.6 nm) and narrow particle size distribution, but the colloids featured different ratios of Au(I)/Au(0) by X-ray photoelectron spectroscopy (XPS). Furthermore, the NHC@AuNPs were supported on titania and fully characterized. The new NPs were studied for their catalytic activity towards the reduction of nitrophenol substrates, the reduction of resazurin and for their photothermal efficiency. Initial results on their application in photothermal therapy (PTT) were obtained in human cancer cells in vitro. The aforementioned reactions represent important model reactions towards wastewater remediation, bioorthogonal transformations and cancer treatment.     

1‐Alkynyltriazenes as Functional Analogues of Ynamides

The chemical reactivity of 1‐alkynyltriazenes has been investigated and is found to parallel the reactivity of ynamides. The similarity in reactivity of these two classes of compounds is demonstrated by addition reactions with acids, by cycloaddition reactions with ketenes, tetracyanoethene, and cyclopropanes, as well as by intramolecular cyclization reactions. The presence of reactive triazene groups in the products enables subsequent transformations. Overall, our results suggest that 1‐alkynyltriazenes should become valuable reagents in synthetic organic chemistry.     

Operations Research challenges in forestry: 33 open problems

Annals of Operations Research - Forestry has contributed many problems to the Operations Research (OR) community. At the same time, OR has developed many models and solution methods for use in...