Lower Bounds for Fixed Spectrum Frequency Assignment

Determining lower bounds for the sum of weighted constraint violations in fixed spectrum frequency assignment problems is important in order to evaluate the performance of heuristic algorithms. It is well known that, when adopting a binary constraints model, clique and near-clique subproblems have a dominant role in the theory of lower bounds for minimum span problems. In this paper we highlight their importance for fixed spectrum problems. We present a method based on the linear relaxation of an integer programming formulation of the problem, reinforced with constraints derived from clique-like subproblems. The results obtained are encouraging both in terms of quality and in terms of computation time.     

Crystal Structures of Hexameric and Dimeric Complexes of Lithioisobutyrophenone

Abstract The crystal structures of two unsolvated hexameric complexes and one N,N,N′,N′-tetramethyl-1,2-ethanediamine (TMEDA)-solvated dimeric complex of the lithium enolate of 2-methyl-1-phenyl-1-propanone (lithioisobutyrophenone, LiIBP) are reported. The unsolvated LiIBP complexes crystallize from benzene-d ₆ to yield two different types of crystals that have similar structures: one in the triclinic space group P-1 with a = 10.7944(7), b = 11.9350(8), c = 12.0956(8) ?; α = 117.5560(10), β = 100.8090(10), γ = 92.3030(10)° and Z = 1 and a second in the monoclinic space group C2/c with a = 17.6011(11), b = 14.7389(9), c = 21.0943(13) ?; β = 105.2510(10)° and Z = 4. The two LiIBP hexamers differ slightly in the conformations of the enolate moieties around the Li₆O₆ core. The hexamer in both the triclinic as well as the monoclinic polymorph is located on a crystallographic inversion center that each generates the other half of the cluster. The TMEDA-solvated LiIBP dimer crystallizes from hexanes in the monoclinic space group C2/c with a = 11.8472(6), b = 14.8268(7), c = 19.2719(9) ?; β = 98.8480(10)° and Z = 4. The center of the dimer is located on a crystallographic C2 axis. These complexes represent only the second reported crystal structures of either an unsolvated hexamer or a solvated dimer of a lithium enolate of a simple monocarbonyl ketone. Graphical Abstract The X-ray crystal structures of two unsolvated hexameric and one N,N,N′,N′-tetramethyl-1,2-ethanediamine (TMEDA)-solvated complexes of the lithium enolate of 2-methyl-1-phenyl-1-propanone (lithioisobutyrophenone, LiIBP) are reported. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Preparation and Reactivity of 4,4′-diaminostilbene-2,2′disulphonate

The precursor compound 4,4′-diaminostilbene-2,2′disulphonic acid DAS-(SO₃H)₂ was successfully deprotonated through reactions with (n-Bu₄N)(OH) and NaOH to produce the corresponding salts sodium 4,4′-diaminostilbene-2,2′disulphonate Na₂(DAS-(SO₃)₂) (1) and tetrabutylammonium 4,4′-diaminostilbene-2,2′disulphonate (n-Bu₄N)₂(DAS-(SO₃)₂) (2). The structure of (n-Bu₄N)₂(DAS-(SO₃)₂) (2) was confirmed through the use of single crystal X-ray diffraction. Compound (2) crystallizes in the monoclinic space group P2₁/n with the lattice parameters of a = 10.0645(6), b = 14.2573(9), c = 17.6053(11), and β = 94.3160(10). The reaction of Cu²⁺(aq) with (n-Bu₄N)₂(DAS-(SO₃)₂) resulted in the crystallization of the molecular organocopper cluster, [CuDAS-(SO₃)₂]₂·3H₂O (3), that resembles a molecular parallelogram as revealed by single crystal X-ray diffraction. Compound (3) crystallizes in the monoclinic space group P2₁/n with the lattice parameters of a = 8.8647(6), b = 10.5247(7), c = 21.2265(14), and β = 93.1730(10). Within the structure of (3) each [DAS-(SO₃)₂]²⁻ ligand is shown to bind two copper atoms through interactions with three of the five available metal binding sites.

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Graphical abstract Preparation and Reactivity of 4,4′-diaminostilbene-2,2′disulphonate Natalie C. Rader, Heather A. Nees, Paul S. Szalay*, Matthias Zeller and Allen D. Hunter The preparation of 4,4′-diaminostilbene-2,2′disulphonic and its reactivity with copper(II) are described.

     

Discovery of Highly Selective Alkyne Semihydrogenation Catalysts Based on First‐Row Transition‐Metallated Porous Organic Polymers

Five different first‐row transition metal precursors (V^III, Cr^III, Mn^II, Co^II, Ni^II) were successfully incorporated into a catechol porous organic polymer (POP) and characterized using ATR‐IR and XAS analysis. The resulting metallated POPs were then evaluated for catalytic alkyne hydrogenation using high‐throughput screening techniques. All POPs were unexpectedly found to be active and selective catalysts for alkyne semihydrogenation. Three of the metallated POPs (V, Cr, Mn) are the first of their kind to be active single‐site hydrogenation catalysts. These results highlight the advantages of using a POP platform to develop new catalysts which are otherwise difficult to achieve through traditional heterogeneous and homogeneous routes.     

Modelling the behaviour of unemployment rates in the US over time and across space

This paper provides evidence that unemployment rates across US states are stationary and therefore behave according to the natural rate hypothesis. We provide new insights by considering the effect of key variables on the speed of adjustment associated with unemployment shocks. A highly-dimensional VAR analysis of the half-lives associated with shocks to unemployment rates in pairs of states suggests that the distance between states and vacancy rates respectively exert a positive and negative influence. We find that higher homeownership rates do not lead to higher half-lives. When the symmetry assumption is relaxed through quantile regression, support for the Oswald hypothesis through a positive relationship between homeownership rates and half-lives is found at the higher quantiles.     

Characterization of Epoxy Glues with FTIR

Abstract

Adhesives have been used since ancient times, but in the mid-19509, when new polymeric adhesives were introduced, the concept of glues changed dramatically. These new adhesives have become the predominant method for fastening materials together. Adhesive glues can be classified as thermoplastic o r thermosetting. The thermoplastic category includes hot melts, cyanoacrylates, solutions (acetates, acrylics), and dispersions (synthetic rubber, latex). Thermoplastics soften when heated, are soluble in at least a few solvents, and tend to creep (undergo permanent change in dimension) under stress. They are composed of long linear chains lying together, but the three dimensions are not interconnected. On the other hand, thermosetting adhesives do not deform readily. They are insoluble in nearly all solvents, so analysis is difficult. The polymer chain segments are cross linked in all three dimensions, making deformation difficult o r impossible at room temperature. In addition to phenolics, polyurethanes, and silicones, epoxies are classified as thermosetting adhesives. Epoxy glues are used to bond metals, glass, ceramics, plastics, wood, concrete, and many other surfaces. Their strength, versatility, and excellent adhesion to a variety of surfaces in addition to their ease of use have made epoxies an important commercial product as well as invaluable to industry [1].     

High‐resolution slice selection NMR for the measurement of CO2 diffusion under non‐equilibrium conditions

We present a simple and an efficient approach using spatially selective NMR to investigate solvation and diffusion of CO₂ in ionic liquids. The techniques demonstrated here are shown as novel and effective means of studying solvated gas dynamics under non‐equilibrium conditions without the need for conventional high power gradients. Copyright © 2014 John Wiley & Sons, Ltd.