Synergistic surfactant mixtures containing lignosulphonates

Enhanced oil recovery (EOR) schemes have been gaining importance over the past several years. Of the various methods being tested, surfactant (or micellar) flooding appears to be one of the most promising ones. It involves injecting into the well the solution of a surfactant which reduces the inter-facial tension between the displacing aqueous solution and the oil trapped in the reservoir. Depending on the concentration of the surfactant, oil displacement proceeds either by a miscible process (surfactant concentration > 10%) or by a immiscible process (surfactant concentration = 2–3%). Miscible flooding converts to the immiscible process as the system is diluted by connate (interstitial) water. Under immiscible conditions, the most significant parameter affecting recovery is the interfacial tension^(1,2). Petroleum sulfonates are perhaps the most important group of surfactants capable of producing very low interfacial tensions between crude oil and the water phase. Their relatively high cost, however, renders many potential applications uneconomical.     

Separable algorithms for distance transformations on irregular grids

In this article, we propose to investigate two extensions of the E²DT (squared Euclidean Distance Transformation) on irregular isothetic grids (or I-grids), such as quadtree/octree or run-length encoded d-dimensional images. We enumerate the advantages and drawbacks of the I-CDT, based on the cell centres, and the ones of the I-BDT, which uses the cell borders. One of the main problem we mention is that no efficient algorithm has been designed to compute both transforms in arbitrary dimensions. To tackle this problem, we describe in this paper two algorithms, separable in dimension, to compute these distance transformations in the two-dimensional case, and we show that they can be easily extended to higher dimensions.     

Automated parameter estimation of the Hodgkin-Huxley model using the differential evolution algorithm: application to neuromimetic analog integrated circuits

We propose a new estimation method for the characterization of the Hodgkin-Huxley formalism. This method is an alternative technique to the classical estimation methods associated with voltage clamp measurements. It uses voltage clamp type recordings, but is based on the differential evolution algorithm. The parameters of an ionic channel are estimated simultaneously, such that the usual approximations of classical methods are avoided and all the parameters of the model, including the time constant, can be correctly optimized. In a second step, this new estimation technique is applied to the automated tuning of neuromimetic analog integrated circuits designed by our research group. We present a tuning example of a fast spiking neuron, which reproduces the frequency-current characteristics of the reference data, as well as the membrane voltage behavior. The final goal of this tuning is to interconnect neuromimetic chips as neural networks, with specific cellular properties, for future theoretical studies in neuroscience.     

A Memetic Algorithm for staff scheduling problem in airport security service

The staff scheduling problem is widely studied in Operational Research. Various surveys are available in the literature dealing with this problem which concerns various objectives and various constraints. In this article, we present a staff scheduling problem in airport security service. First, a modeling of the problem, and a representation of solutions are shown. The problem is solved in three steps, days-off scheduling, shift scheduling, and staff assignment. We focus on the last step, by providing a Memetic Algorithm (MA) which merged an Evolutionary Algorithm and Local Search techniques. We propose a chromosome encoding, a crossover operator and a combined neighborhood function, specially dedicated to this staff assignment problem. Besides providing better solutions than software currently used, this algorithm provides up to 50% of improvement from initial feasible solutions.     

Recent Advances in Boron Nitride Nanotubes and Nanosheets

Herein the recent experiments performed by the authors on fabricated multi-walled BN nanotubes and monoatomic BN graphene-like nanosheets are reviewed. The results are presented in several sections, namely: (i) method for high-yield synthesis of thin, defect-free BN nanotubes of only a few-layers, with external diameters below 10 nm; (ii) verification of BN nanotube piezoelectrical behavior and its electrically-induced thermal decomposition under combined resistive heating and electrical charging in a transmission electron microscope; (iii) the first direct measurements of the true tensile strength and Young’s modulus of BN nanotubes, using newly developed nanotensile tests inside an electron microscope; the measured values were found to be ∼30 GPa and ∼900 GPa, respectively; and (iv) diverse kinetic processes taking place within the prepared monoatomic BN sheets (so-called “white graphenes”) affiliated with intensive knock-on B and N atom displacements under high energy electron beam irradiation in an aberration-corrected medium-voltage high-resolution transmission electron microscope.     

Plasma Modifications to the Interface in Carbon Fiber Reinforced Thermoplastic Matrices

Radio frequency glow discharge oxygen plasma was used to modify the surfaces of PAN-based and mesophase pitch-based carbon fibers. Surface chemical changes to the fibers were monitored by X-ray photoelectron spectroscopy and by fiber wetting studies evaluated in terms of dispersive-polar components of surface energy and acid-base contribution to the work of adhesion. Physical changes to these fibers were monitored by scanning electron microscopy. Stress transferability of these fibers was evaluated by the embedded single fiber test in poly(methyl methacrylate), poly(ethyl methacrylate), poly(methacrylonitrile) and poly(vinyl chloride) as these matrices offered varying degrees of dispersive-polar and acid-base character. Experimentally determined critical aspect ratios were compared to the theoretical work of adhesion determined by dispersive-polar interactions and with the Lewis acid-base nature of the matrices.     

Dissolution mechanism of 316L in lead–bismuth eutectic at 500 °C

In the frame of the Accelerator Driven System (ADS) cooled by liquid lead–bismuth eutectic (LBE), the austenitic stainless steel 316L is considered as a possible structural material for the reactor. However, the corrosion of 316L in this liquid alloy environment can be substantial, especially when a dissolution process occurs. In order to understand the dissolution process and to obtain a modelling of the 316L corrosion rate by LBE, an experimental dissolution kinetics of 316L is carried out in stagnant LBE at 500 °C up to 3000 h. A Ni preferential dissolution of the 316L is observed, leading to the formation of a ferritic layer at the 316L surface. A discussion on the various steps occurring in dissolution process leads to the conclusion that only the Ni dissolution reaction rate can control the 316L dissolution kinetics. The dissolution reaction rate constant, k_d, calculated from this study experimental points is equal to 4.2 × 10⁻¹¹ mol cm⁻² s⁻¹.     

Reduced graphene oxide

This paper describes a novel approach to the preparation of reduced graphene oxide and its dispersions in organic solvents. Graphite oxide, graphene oxide, and reduced graphene oxide have been prepared and characterized by a variety of physicochemical techniques.     

Microdeformation mechanisms in rubber toughened PMMA and PMMA-based copolymers

The classical method of toughening polymethylmethacrylate (PMMA) is to incorporate composite rubber particles into the homopolymer matrix. This approach has been extended in the present work by (i) combining rubber toughening with chemical modification of the matrix or (ii) introduction of the rubber modifier via PMMA-b-polybutylacrylate (PBA)-b-PMMA triblock copolymers. Significant improvements in fracture toughness at low speeds were observed in notched compact tension tests when the ductility of the rubber toughened PMMA matrix was improved by copolymerization, and comparable levels of toughness were achieved in the block copolymers. However, both types of material showed a transition to more brittle behavior at impact speeds, associated with increased localization of the crack tip deformation. Physical interpretations for this behavior and the scope for further optimization of the fracture response are discussed.