Branch-and-Sandwich: a deterministic global optimization algorithm for optimistic bilevel programming problems. Part I: Theoretical development

We present a global optimization algorithm, Branch-and-Sandwich, for optimistic bilevel programming problems that satisfy a regularity condition in the inner problem. The functions involved are assumed to be nonconvex and twice continuously differentiable. The proposed approach can be interpreted as the exploration of two solution spaces (corresponding to the inner and the outer problems) using a single branch-and-bound tree. A novel branching scheme is developed such that classical branch-and-bound is applied to both spaces without violating the hierarchy in the decisions and the requirement for (global) optimality in the inner problem. To achieve this, the well-known features of branch-and-bound algorithms are customized appropriately. For instance, two pairs of lower and upper bounds are computed: one for the outer optimal objective value and the other for the inner value function. The proposed bounding problems do not grow in size during the algorithm and are obtained from the corresponding problems at the parent node.     

Facilitated modelling with discrete-event simulation: Reality or myth?

Is it possible for discrete-event simulation to be used in a facilitated workshop environment? Over the last decade there have been various attempts to use simulation in this way, but we argue here that none have been successful in achieving a fully facilitated mode where the model is both developed and used in the workshop. We attempt to use a discrete-event simulation in a facilitated mode as part of a lean improvement workshop in a hospital setting. The model was successfully developed and used within the 3 day period of the workshop. Although the intervention was successful, we still had to build the model in the ‘back-office’, meaning that a fully facilitated mode was not achieved. The paper concludes by discussing how fully facilitated modelling with discrete-event simulation might be made possible; the answer is more about changing mind-sets than about technological challenge.     

The resource-constrained modulo scheduling problem: an experimental study

In this paper, we focus on the resource-constrained modulo scheduling problem (RCMSP), a general periodic scheduling problem, abstracted from the problem solved by compilers when optimizing inner loops at instruction level for VLIW parallel processors. Heuristic solving scheme have been proposed since many years to solve this problem, among which the decomposed software pipeling method. In this method, a cyclic scheduling problem ignoring resource constraints is first considered and a so-called legal retiming of the operations is issued. Second, a standard acyclic problem, taking this retiming as input, is solved through list scheduling techniques. In this paper, we propose a novel hybrid approach, which uses the decomposed software pipeling method to obtain a good retiming. Then the obtained retiming is used to build an integer linear programming formulation of reduced size, which allows to solve it exactly. Experimental results show that a lot more problems are solved with this new approach. The gap to the optimal solution is less than 1 % on most of the tested problem instances and the method appears to be competitive with a recently proposed constraint programming algorithm (Bonfietti et al., Lect. Notes Comput. Sci. 6876:130–144, 2011).     

A multiscale poromicromechanical approach to wave propagation and attenuation in bone

Ultrasonics is an important diagnostic tool for bone diseases, as it allows for non-invasive assessment of bone tissue quality through mass density–elasticity relationships. The latter are, however, quite complex for fluid-filled porous media, which motivates us to develop a rigorous multiscale poromicrodynamics approach valid across the great variety of different bone tissues. Multiscale momentum and mass balance, as well as kinematics of a hierarchical double porous medium, together with Darcy’s law for fluid flow and micro–poro-elasticity for the solid phase of bone, give access to the so-called dispersion relation, linking the complex wave numbers to corresponding wave frequencies. Experimentally validated results show that 2.25 MHz acoustical signals transmit healthy cortical bone (exhibiting a low vascular porosity) only in the form of fast waves, agreeing very well with experimental data, while both fast and slow waves transmit highly osteoporotic as well as trabecular bone (exhibiting a large vascular porosity). While velocities and wavelengths of both fast and slow waves, as well as attenuation lengths of slow waves, are always monotonously increasing with the permeability of the bone sample, the attenuation length of fast waves shows a minimum when considered as function of the permeability.     

Inside the glassmaker technology: search of Raman criteria to discriminate between Emile Gallé and Philippe‐Joseph Brocard enamels and pigment signatures

The development of solid‐state chemistry at the end of the 19th century offered a variety of routes to colour a glass matrix. Eight enamelled glass objects made by Philippe‐Joseph Brocard and two representative objects made by Emile Gallé have been analysed using a mobile Raman instrument at the Musée des arts décoratifs (Paris) in order to compare their colouration technology. White, blue, yellow, green, orange, red, brown and black pigments have been identified. If most of the pigment palette is common to both craftsmen and typical of the second half of the 19th century, innovative uses are recognized for Gallé (wollastonite as an opacifier, manganese oxides in black mixtures) and Brocard (specific black and grey, pigment mixture, shade modification by small addition of white and red pigments). This preliminary work confirms the potential of Raman spectroscopy, not as a simple analytical method but as a way to document the ancient technology of fine art objects and to discriminate between different genuine productions and/or copies. Copyright © 2014 John Wiley & Sons, Ltd.     

Orientation-dependent recovery in strongly deformed Al–0.1% Mn crystals

Single crystals of Al–0.1% Mn were channel-die compressed to a true strain of 2.3 and their recovery behaviour at 240–320°C investigated by microhardness measurements, electron backscatter diffraction (EBSD) microtexture mapping and X-ray line broadening analysis. The crystal orientations were the nominally stable Goss {110}?001?, brass {110}?112? and S {123}?634?. For all three orientations the microhardness decreases with a logarithmic time dependence but the instantaneous recovery rates of the brass oriented crystals are systematically lower than those of the other two orientations by a factor of about 2. The dislocation densities decrease rapidly in the first stages of recovery (<1?min) by dislocation dipole annihilation and more slowly thereafter. In the Goss and S orientations the later stage of recovery is due to sub-grain growth. The orientation dependence is ascribed to the relatively low misorientations developed by plastic straining in the brass crystals (average about 4°) compared with the Goss and S orientations (about 7–8°).     

Rigorous determination of the stoichiometry of protein phosphorylation using mass spectrometry

Quantification of the stoichiometry of phosphorylation is usually achieved using a mixture of phosphatase treatment and differential isotopic labeling. Here, we introduce a new approach to the concomitant determination of absolute protein concentration and the stoichiometry of phosphorylation at predefined sites. The method exploits QconCAT to quantify levels of phosphorylated and nonphosphorylated peptide sequences in a phosphoprotein. The nonphosphorylated sequence is used to determine the absolute protein quantity and serves as a reference to calculate the extent of phosphorylation at the second peptide. Thus, the stoichiometry of phosphorylation and the absolute protein concentration can be determined accurately in a single experiment.     

Effect of ruthenium substitution in layered sodium cobaltate NaxCoO2: Synthesis, structural and physical properties

Solid-state synthesis of Na_0.71Co_1−xRu_xO₂ compositions shows that ruthenium can be substituted for cobalt in the hexagonal Na_0.71CoO₂ phase up to x=0.5. The cell expands continuously with increasing ruthenium content. All mixed Co-Ru phases show a Curie-Weiss behaviour with no evidence of magnetic ordering down to 2 K. Unlike the parent phase Na_0.71CoO₂, ruthenium-substituted phases are all semiconducting. They exhibit high thermoelectric power, with a maximum of 165 μV/K at 300 K for x=0.3. The Curie constant C and Seebeck coefficient S show a non-monotonic evolution as a function of ruthenium content, demonstrating a remarkable interplay between magnetic properties and thermoelectricity. The presence of ruthenium has a detrimental effect on water intercalation and superconductivity in this system. Applying to Ru-substituted phases the oxidative intercalation of water known to lead to superconductivity in the Na_xCoO₂ system yields a 2-water layer hydrate only for x=0.1, and this phase is not superconducting down to 2 K.     

Coordination environment of [UO2Br4] in ionic liquids and crystal structure of [Bmim]2[UO2Br4]

The complex formed by the reaction of the uranyl ion, UO₂²⁺, with bromide ions in the ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][Tf₂N]) and methyl-tributylammonium bis(trifluoromethylsulfonyl)imide ([MeBu₃N][Tf₂N]) has been investigated by UV–Vis and U L_III-edge EXAFS spectroscopy and compared to the crystal structure of [Bmim]₂[UO₂Br₄]. The solid state reveals a classical tetragonal bipyramid geometry for [UO₂Br₄]²⁻ with hydrogen bonds between the Bmim⁺ and the coordinated bromides. The UV–Vis spectroscopy reveals the quantitative formation of [UO₂Br₄]²⁻ when a stoichiometric amount of bromide ions is added to UO₂(CF₃SO₃)₂ in both Tf₂N-based ionic liquids. The absorption spectrum also suggests a D_4h symmetry for [UO₂Br₄]²⁻ in ionic liquids, as previously observed for the [UO₂Cl₄]²⁻ congener. EXAFS analysis supports this conclusion and demonstrates that the [UO₂Br₄]²⁻ coordination polyhedron is maintained in the ionic liquids without any coordinating solvent or water molecules. The mean U–O and U–Br distances in the solutions, determined by EXAFS, are, respectively, 1.766(2) and 2.821(2) Å in [Bmim][Tf₂N], and, respectively, 1.768(2) and 2.827(2) Å, in [MeBu₃N][Tf₂N]. Similar results are obtained in both ionic liquids indicating no significant influence of the ionic liquid cation either on the complexation reaction or on the structure of the uranyl species.     

Aluminium Mediated Glycosaminoglycan/Amyloid-β Association Mechanism

In Alzheimer’s disease, it has been proposed that glycosaminoglycans facilitate amyloid fibril formation and/or stabilize the plaque aggregates. Chondroitin sulfates are sulfated glycosaminoglycans represented an ideal distribution of charge for amyloid-β (Aβ) interactions. Recent studies have suggested a possible link between the neurotoxicity of aluminum and the pathogenesis of Alzheimer’s disease. In this paper, the interaction of Aβ with chondroitin sulfates immobilized on a chromatographic column and the role of aluminum had been studied using a biochromatographic approach (molecular chromatography). A novel biochromatographic column was developed in our laboratory for studying this interaction. This study demonstrated that the aluminum interacted with Aβ and played a role in the Aβ/chondroitin sulfates association. For a Al³⁺ concentration (x) in the medium less than 30 μmM, the Aβ/chondroitin sulfates binding decreased with x due to a decrease of the charge–charge interactions between Aβ and its chondroitin sulfates binding site. Above 30 μmM of Al³⁺ in the medium, the affinity of Aβ to chondroitin sulfates increased slightly with x because the net number of ions (n) (Al³⁺ or Cl^?) released or bound upon complex formation is low. As well, it was clearly demonstrated, that above 30 μmM the n value depend on the Al³⁺ concentration in the bulk solvent. This dependence was due to a gradual and conformational change of the Aβ which around 80 μmM adopted a less flexible structure; its binding site was thus less accessible to Aβ and Aβ/chondroitin sulfates association decreased slightly.