Model and methods to address urban road network problems with disruptions

Disruptions in urban road networks can quickly and significantly reduce the quality of the whole transportation network, and impact urban mobility for light vehicles, public transportation, etc. In this study, we consider both unidirectional and multidirectional road network problems with disruptions and connecting requirements. These problems aim at reconfiguring the urban network in terms of road direction in order to maintain a path among all points of the network (strong connectivity). The former is defined on simple graphs, mainly modeling part of a city such as historical centers, while the latter relies on multigraphs, modeling more general networks. Restoring the network (strong connectivity) after some disruptions may require the modification of the orientation of some streets, that is, arc reversals. Such actions can disturb users' driving habits. Thus, two objectives are considered separately: minimizing the total travel distance and minimizing the number of arc reversals. We define formally both problems and propose two metaheuristics, a biased random key genetic algorithm and an iterated local search. Numerical experiments have been performed on a set of generated instances and on the urban network of Troyes (France).     

Encoding Information on the Excited State of a Molecular Spin Chain

The quantum states of nano-objects can drive electrical transport properties across lateral and local-probe junctions. This raises the prospect, in a solid-state device, of electrically encoding information at the quantum level using spin-flip excitations between electron spins. However, this electronic state has no defined magnetic orientation and is short-lived. Using a novel vertical nanojunction process, these limitations are overcome and this steady-state capability is experimentally demonstrated in solid-state spintronic devices. The excited quantum state of a spin chain formed by Co phthalocyanine molecules coupled to a ferromagnetic electrode constitutes a distinct magnetic unit endowed with a coercive field. This generates a specific steady-state magnetoresistance trace that is tied to the spin-flip conductance channel, and is opposite in sign to the ground state magnetoresistance term, as expected from spin excitation transition rules. The experimental 5.9 meV thermal energy barrier between the ground and excited spin states is confirmed by density functional theory, in line with macrospin phenomenological modeling of magnetotransport results. This low-voltage control over a spin chain's quantum state and spintronic contribution lay a path for transmitting spin wave-encoded information across molecular layers in devices. It should also stimulate quantum prospects for the antiferromagnetic spintronics and oxides electronics communities.     

Room temperature molten salts as lithium battery electrolyte

In the present study, are reported investigations obtained with the room temperature molten salt (RTMS) ethyl-methyl-imidazolium bis-(trifluoromethanesulfonyl)-imide (EMI-TFSI) in order to use it as solvent in lithium battery. The thermal stability, viscosity, conductivity and electrochemical properties are presented. A solution of 1m lithium bis-(trifluoromethanesulfonyl)-imide (LiTFSI) in EMI-TFSI has been used to test the electrolyte in a battery with LiCoO₂ and Li₄Ti₅O₁₂ as respectively cathode and anode materials. Cycling and power measurements have been obtained. The results have been compared with those obtained with a molten salt formulated with a different anion, BF₄⁻ and with a conventional liquid organic solvent EC/DMC containing LiTFSI. The 1m LiTFSI/EMI-TFSI electrolyte provides the best cycling performance: a capacity up to 106 mAh g⁻¹ is still delivered after 200 cycles, with 1C rate at 25 °C.     

Development and Pheromone Communication Systems in Hybrids of Agrotis ipsilon and Agrotis segetum (Lepidoptera: Noctuidae)

Hybrids were obtained by crossing males of the turnip moth Agrotis segetum, which has a period of arrested development in the larval stage, with females of the migrant and nondiapausing black cutworm, Agrotis ipsilon. No progeny were obtained by crossing females of A. segetum with males of A. ipsilon. Backcrosses were successful only by crossing hybrids with both sexes of A. ipsilon. No larval oligopause occurred when hybrid larvae were reared under conditions inducing arrest in A. segetum (12L:12D, 21°C). Wind tunnel tests showed interattractiveness of F₁ hybrids with A. ipsilon but not with A. segetum. Single sensillum recordings of pheromone-sensitive hairs on the antennae of males of the parent species revealed differences in the distribution of sensilla. F₁ and F₂ hybrids exhibited the same receptor cell types and distribution as A. ipsilon. Gas chromatographic analysis of female pheromone gland extracts revealed that F₁ hybrids were also very close to A. ipsilon.     

Species-specific stable isotope analysis by the hyphenation of chromatographic techniques with MC-ICPMS

This work reviews the basis and all the existing publications on the hyphenation of chromatography-based techniques to MC-ICPMS for isotopic studies that were published until the end of 2010. A brief historical retrospective of the measurement of isotope ratios from transient signals by ICPMS with different sample introduction techniques is also included. The most important experimental parameters and data reduction strategies affecting the accurate and precise measurement of compound-specific isotope ratios by either HPLC or GC coupled to MC-ICPMS are discussed. All the applications are reported and critically reviewed in terms of analytical characteristics, performances, optimization, advantages and disadvantages and future applicability to the environmental, geochemical, or bioinorganic studies.     

Iso-scallop tool path generation in 5-axis milling

This paper presents a new method of computing constant scallop height tool paths in 5-axis milling on sculptured surfaces. Usually, iso-scallop tool path computation methods are based on approximations. The attempted scallop height is modelled in a given plane to ensure a fast computation of the tool path. We propose a different approach, based on the concept of the machining surface, which ensures a more accurate computation. The machining surface defines the tool path as a surface, which applies in 3- or 5-axis milling with the cutting tools usually used. The machining surface defines a bi-parametric modelling of the locus of a particular point of the tool, and the iso-scallop surface allows to easily find iso-scallop tool centre locations. An implementation of the algorithms is done on a free-form surface with a filleted end mill in 5-axis milling.     

The effect of aluminum alkyls and BHT‐H on reaction kinetics of silica supported metallocenes and polymer properties in slurry phase ethylene polymerization

In slurry and gas phase catalytic ethylene polymerization processes, aluminum alkyl (AlR₃) compounds are usually present inside the reactor and their role either as co‐catalyst or scavenger is of considerable importance. Silica supported metallocene/methyl aluminoxane (MAO) catalysts show specific interactions with AlR₃ compounds. Therefore, this study shows an attempt to analyze and compare the effect of concentration as well as type of commonly used AlR₃ on slurry phase ethylene homopolymerization kinetics of silica supported (n‐BuCp)₂ZrCl₂/MAO catalyst. The obtained results indicate that the lower the concentration of smaller AlR₃ compounds, the higher the instantaneous catalytic activity. Concerning the polymer particle size distributions, a rise in fines generation has been observed with increasing AlR₃ content inside the reactor. Finally, it has been shown that the addition of 2,6‐di‐tert‐butyl‐4‐methylphenol (a substituted phenol) into the reactor containing AlR₃ reduces the influence of AlR₃ compounds on the reaction kinetics of silica supported metallocene/MAO catalysts. Polyethylene properties remain similar in all the studied scenarios. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45670.     

Experimental proof of the existence of mass‐transfer resistance during early stages of ethylene polymerization with silica supported metallocene/MAO catalysts

The size of a silica supported metallocene/MAO (methylaluminoxane) catalyst plays an important role in determining its productivity during ethylene polymerization. From a chemical engineering point of view, this size dependency of catalytic activity of supported metallocenes is mathematically connected with the different levels of mass‐transfer resistance in big and small catalyst particles but no experimental evidence has been provided to date. The results of this systematic experimental study clearly demonstrate that the intraparticle monomer diffusion resistance is high in bigger catalyst particles during initial instants of ethylene polymerization and diminishes with the polymer particle growth. Two different silica supported metallocene/MAO catalysts provided the same results while highlighting the fact that catalyst chemistry should be carefully considered while studying complex chemical engineering problems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4476–4490, 2017     

Two‐dimensional modeling of an absorbing falling film in its development zone

This work presents the modeling of a vertical falling film expanding or shrinking from the inlet manifold. Considering a stationary approach, the film shape, the flow field and the absorption rate of an ambient gas are computed. For the flow field, one dimensional (1‐D) second‐order weighted integral boundary layer (WIBL) model is shown to accurately reproduce the film deformations. The gas transfer is then solved in a 2‐D predeformed domain to investigate the impact of the film deformations on the gas absorption rate. It is found that a significant mass transfer enhancement, as compared to a flat film, is obtained when the film is expanding due to the concomitant increase of the concentration gradient perpendicular to the interface. On the contrary, a slight hindrance of the mass transfer is observed when the film is shrinking, although it remains in this case very close to the flat film analytical solution. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4370–4378, 2017