Three-stage hybrid-flowshop model for cross-docking

This paper deals with the optimization of a cross-docking system. It is modeled as a three-stage hybrid flowshop, in which shipments and orders are represented as batches. The first stage corresponds to the receiving docks, the second stage corresponds to the sorting stations, and the third stage corresponds to the shipping docks. The objective of the problem is to find a schedule that minimizes the completion time of the latest batch. In order to obtain good quality feasible solutions, we have developed several heuristic schemes depending on the main stage considered, and several rules to order the batches in this stage. Then, we propose a branch-and-bound algorithm that takes into account the decomposition of the problem into three stages. To evaluate the heuristics and to reduce the tree size during the branch-and-bound computation, we also propose lower bounds. Finally, the computational experiments are presented to demonstrate the efficiency of our heuristics. The results show that the exact approach can solve instances containing up to 9–10 batches in each stage (i.e., up to 100 jobs). In addition, our heuristics were evaluated over instances with up to 3000 jobs, and they can provide good quality feasible solutions in a few seconds (i.e., less than 2 s per heuristic).     

Removal of NOx: Part II. Species formed during the sorption/desorption processes on barium aluminates

The formation of various species formed during the adsorption of NO_x issued from a synthetic lean-burn exhaust gas upon barium aluminates was studied using FTIR and TGA. The results have been systematically compared to those obtained with bulk BaO. Two factors are responsible for the difference observed during adsorption/desorption tests on the two solids. On one hand, stable carbonates are formed on BaO whereas no carbonate is formed on barium aluminate. On the other hand, the structure of the nitrates formed on these two compounds is very different, an N-bounded nitrate is formed on barium aluminate and not on bulk BaO.     

Effect of Ba doping on performance of LST as anode in solid oxide fuel cells

The level of barium doping in lanthanum strontium titanate (La_0.4Sr_0.6−xBa_xTiO₃, 0 ≤ x ≤ 0.2; LST, x = 0; LSBT, x > 0), prepared by solid state synthesis, affects its performance as anode in solid oxide fuel cells (SOFCs). Cell structures of LST and all LSBT were similar. The oxidation state of Ti in all compounds was reduced by a comparable amount when LST or LSBT was heated under reducing conditions to form La_0.4Sr_0.6−xBa_xTi_0.59⁴⁺Ti_0.41³⁺O_2.97. All fuel cells using LST or LSBT had high activity for conversion of hydrogen or methane, and the activity increased with the level of substitution by Ba. In addition, performance was enhanced when H₂S was present in either CH₄ or H₂ fuel. There was good contact between YSZ electrolyte and each LSBT or LSB anode.     

ATM local area networks: a survey of requirements, architectures,and standards

There is increasing interest in deploying ATM technology in local or campus networks. ATM is an ideal technology to overcome many of the limitations of today's LAN technologies. This article focuses on the application of ATM in the LAN environment to interconnect high-end host computers, and on the interworking of ATM-based LANs with legacy LANs. The authors introduce ATM LAN requirements, followed by a discussion of possible ATM LAN architectures to support these requirements. The article then covers current standards and their relation to the possible architectures, and concludes with a discussion of current ATM LAN issues and directions     

The mini-conical slump flow test: Analysis and numerical study

This paper provides a general study on cement paste flow. Both mini-slump and Marsh cone tests are used to evaluate the workability of fresh paste mixtures derived from self compacting concretes. A numerical approach is used to reproduce global flow behavior and to check the accuracy of the obtained viscosity as well as the validity of expressions available in the literature giving yield stress from the final diameter of slumped paste. The computational modeling allows access to local information in order to analyze different regions and corresponding flow types, i.e. falling solid and flowing fresh cementing material mixtures.The limitation of some empirical models allowing the prediction of yield stress τ₀ and plastic viscosity μ from mini-slump tests is underlined, conditions of validity are expressed and a new expression is proposed.     

Helical metallomacrocyclic nickel(II) complexes of a tetradentate N2S2 ligand derived from N-methyldithiocarbazic acid

The structure of the tetradentate sulphur–nitrogen chelating agent, 1,2-phenylenebis(methylene) bis(1-methylhydrazinecarbodithioate) (NSSN) has been determined by X-ray diffraction. In the solid state, the two arms of the ligand remain in E configurations about the hydrazinic C–N bonds. The ligand reacts with hydrated nickel(II) salts in a 3:2 ligand-to-metal ratio yielding dimeric triple helical complexes of general formula, [Ni₂(NSSN)₃]X₄·nH₂O (X = Cl, Br, I, NCS; n = 5, 6, 9) which contain two nickel(II) ions in distorted octahedral environments. An X-ray crystallographic structure determination of the [Ni₂(NSSN)₃]Cl₄·9H₂O complex shows that it is a metallomacrocycle in which each ligand acts as a bis-bidentate chelating agent providing NS donors of one arm to one nickel(II) ion and NS donors of the second arm to a second nickel(II) ion. Each nickel(II) ion adopts a distorted octahedral geometry with a NiN₃S₃ coordination core as shown by their common electronic spectra.     

Organocatalyzed Conjugate Addition of Carbonyl Compounds to Nitrodienes/Nitroenynes and Synthetic Applications

The purpose of this study is to point out the synthetic utility of a new class of Michael acceptors (nitrodienes and nitroenynes). The highly enantioselective organocatalytic Michael addition of carbonyl compounds to these functionalized nitroolefins has been carried out in the presence of (S)‐diphenylprolinol silyl ether to achieve some interesting building blocks in high selectivities. The adducts thus obtained can be easily converted by taking advantage of the corresponding unsaturated carbon‐carbon bond. In presence of the double bond, metathesis or electrophilic activation could be carried out whereas in the presence of the triple bond electrophilic activation could be conducted. We thus focused on a gold‐catalyzed cyclization of the bis‐homopropargylic alcohol to afford the corresponding substituted tetrahydrofuran. Then, we also demonstrated that organic and gold catalysts were compatible in a one‐pot process. Indeed, we developed a one‐pot enantioselective organocatalytic Michael addition to a nitroenyne followed by a gold‐catalyzed acetalization/cyclization to achieve tetrahydrofuranyl ethers in high diastereo‐ and enantioselectivities with excellent yields.     

Damage quantification in aluminium alloys using in situ tensile tests in X-ray tomography

This paper presents results obtained using in situ tensile experiments allowing the observation of damage nucleation, growth and coalescence. Three different aluminium alloys (2024, 7449 and 5754) exhibiting various mechanical properties were chosen to produce a wide data base. Smooth and notched axisymetric samples were cut out of the raw materials to introduce different levels of initial stress triaxiality using the geometry of the samples. In the different cases, the damage steps (initiation, growth and coalescence) were clearly visualised during interrupted and continuous in situ tensile tests in synchrotron X-ray tomography. The imaging was performed with a voxel size of 1.6 μm. The X-ray tomography method also gives a precise image of the outer shape of the sample and its change during deformation can then be analysed. This allows to calculate precisely the true strain vs true stress curve and also an approximation of the stress triaxiality using the Bridgman formula. The results show that damage can be visualised but also quantified precisely in the different cases in terms of nucleation and growth, coalescence being also evident in the results but still hard to quantify so far. Finally, a previously developed model for damage growth during ductile straining based on the Rice and Tracey approach can be fitted to the results.