MPI+X: task-based parallelisation and dynamic load balance of finite element assembly

The main computing phases of numerical methods for solving partial differential equations are the algebraic system assembly and the iterative solver. This work focuses on the first task, in the context of a hybrid MPI+X paradigm. The matrix assembly consists of a loop over the elements, faces, edges or nodes of the MPI partitions to compute element matrices and vectors and then of their assemblies. In a MPI+X hybrid parallelism context, X has consisted traditionally of loop parallelism using OpenMP, with different techniques to avoid the race condition, but presenting efficiency or implementation drawbacks. We propose an alternative, based on task parallelism using some extensions to the OpenMP programming model. In addition, dynamic load balance will be applied, especially efficient in the presence of hybrid meshes. This paper presents the proposed methodology, its implementation and its validation through the solution of large computational mechanics problems up to 16k cores.     

Hydrophilic PET surfaces by aminolysis and glycopolymer brushes chemistry

Poly(ethylene terephthalate) (PET) is a semiaromatic thermoplastic polyester used in many fields. For specific applications, controlled of the surface wettability (hydrophily/hydrophoby) could be a great challenge. Aminolysis of PET surfaces with branched polyethylenimine gives amino functional groups on the surface with high grafting density. Then, in a second step, atom transfer radical polymerization (ATRP) initiator was grafted by reaction with 2‐bromoisobutyryl bromide. Surface initiated ATRP of 2‐lactobionamidoethyl methacrylate (LAMA) was performed in solution in the presence of a sacrificial initiator or an appropriate amount of Cu(II) species that act as deactivator. The efficiency of all reactions was confirmed by X‐ray photoelectron spectroscopy. Wetting properties and surface energy were found to vary systematically depending to the type of functionalization and grafting. The quantity of grafted carbohydrate was determined by phenol/sulfuric acid colorimetric titration. The sugar graft density was observed to vary according to the ratio (monomer)/(free initiator). High graft density could be obtained yielding to superhydrophilic polymer brushes. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2689–2697     

From TcVII to TcI; facile syntheses of bis-arene complexes [99(m)Tc(arene)2]+ from pertechnetate

Bis-arene complexes of technetium represent a fundamental class of organometallic compounds. Due to complex synthetic routes, no detailed insights into their properties have been reported so far. Reacting [⁹⁹TcO₄]^– with arenes in the exclusive presence of AlCl₃ gives highly stable [⁹⁹Tc(arene)₂]⁺ in good yields. These complexes have extraordinarily high stabilities, where oxidation is found to occur at potentials higher than +1.3 V and reduction at potentials below –2 V vs. Fc/Fc⁺. The ^99mTc analogues are similarly synthesised by applying a novel ionic liquid extraction pathway. Complexes of ^99mTc with suitably functionalized arenes will represent new building blocks for bioorganometallic pharmaceuticals in molecular imaging.     

Improved utilization for joint HCCA–EDCA access in IEEE 802.11e WLANs

This paper presents a model for improving utilization in IEEE 802.11e wireless LAN via a Markov decision process (MDP) approach. A Markov chain tracking the utilized transmission window for two separate access mechanisms is devised. Subsequently, the action space and the rewards of the MDP are judiciously selected with the aim of improving overall utilization without explicit blocking. The proposed MDP model for 802.11e reveals that proportional allocation of access opportunities improve overall utilization compared to completely randomized access. Simulation results go on to show that a policy that limits HCCA access as a function of channel load improves utilization by an average 8 %. The optimization framework proposed in this paper is promising as a practical decision support tool for resource planning in 802.11e.     

The Role of Hydrogen Bonding and Halogen Bonding in the Polymorphic Structures of 3,5-Dibromo-2,6-diaminopyridinium Bromide

Abstract  

An analysis is made of the supramolecular interactions in the two polymorphic structures of 3,5-dibromo-2,6-diaminopyridinium bromide, with particular emphasis on the roles of hydrogen and halogen bonding. Because of the extensive hydrogen bonding capabilities, hydrogen bonding interactions dominate in both phases. This causes a competition between C–Br···Br–C and C–Br···Br⁻ halogen bonding interactions, with the former dominating in the orthorhombic Pbca phase and the latter in the monoclinic P2₁/c phase. For Pbca phase a = 5.5197(11) ?, b = 15.040(3) ?, c = 23.2555(5) ?, and for P2₁/c phase a = 8.1143(19) ?, b = 14.226(3) ?, c = 8.9005(18) ?, β = 113.18(2)°.     

Synthesis and crystal structures of coordination polymers,networks and complexes of an adamantane shaped phosphorus–nitrogen cage ligand and cuprous chloride

Reactions of cuprous chloride with the phosphorus–nitrogen cage ligand 2,4,6,8,9,10-hexamethyl-2,4,6,8,9,10-hexaaza-1,3,5,7-tetraphosphaadamantane, P₄(NCH₃)₆, in acetonitrile form distinct solids depending on the ligand-to-metal ratio. Three structurally characterized compounds include: a solvated 3-D network of formula [P₄(NCH₃)₆]₂(CuCl)₃(CH₃CN)₂; a “ladder-type” polymer {[μ₂-P₄(NCH₃)₆]₂(CuCl)₂}_∞; and a monomeric complex [P₄(NCH₃)₆]₂CuCl. Thermal decomposition of the solvated network results in formation of two more materials [P₄(NCH₃)₆]₂(CuCl)₃, and [P₄(NCH₃)₆](CuCl)₂ that are not isolated from solution reactions. The variety of products isolated based solely on ligand-to-metal ratio suggest that this system participates in solution equilibria common to many phosphorus(III) ligands and multiple solubility equilibria.