Improvement of Staphylococcus xylosus lipase production through optimization of the culture conditions

The Staphylococcus xylosus strain produces without induction an original lipase named S. xylosus lipase (SXL). Since considerable interest has been given to microbial lipases for biotechnology applications like detergents, food, drugs and pharmaceutical products, improvement of their production is of great importance to reduce the final cost. This goal could be reached through the optimization of several physicochemical culture conditions. Indeed, an appropriate medium was formulated for SXL production. It was composed of 17 g/L pancreatic digest of casein, 2.5 g/L glucose, 6 g/L yeast extract, 0.75 g/L ammonium sulfate corresponding to a C/N ratio of 6, 1 g/L K₂HPO₄ and 1 g/L KH₂PO₄. In such a medium, SXL production reached 42 U/mL. Moreover, the usefulness of such a medium for large‐scale production of SXL was also evidenced in an automated fully controlled 2.6‐L fermenter. It was shown that aeration of the medium, which strongly affected the growth, regulated the lipase synthesis by the produced cells. It was found that when using a dissolved oxygen saturation of the medium of 50%, the SXL production reached 62 U/mL.     

Microstructure,Thermal and Mechanical Behavior of 3D Printed Acrylonitrile Styrene Acrylate

Fused deposition modeling (FDM) is one of the most popular additive manufacturing techniques for polymers. Despite the numerous works on the printability of various types of polymers, there is a lack in understanding the role of the microstructure on the mechanical performance of printed parts. This work aims at addressing this particular point for the case of a polymer that did not receive much attention, namely acrylonitrile styrene acrylate or ASA. This study emphasizes on the effect of the printing temperature on thermal and mechanical performance of printed ASA using differential scanning calorimetry, infra‐red measurements, mechanical testing, X‐ray micro‐tomography, and finite element computation. The experimental results demonstrate a narrow window of printability of ASA based on the thermal response of this polymer during the laying down process. In addition, both experimental and numerical results show an evident loss in the performance that represents one third of the performance of the raw material. Despite this loss, the limited amount of generated porosity and the level of tensile strength of ASA make it a good choice as a feedstock material for FDM compared to other polymers such as acrylonitrile butadiene styrene.     

New Computational Model Based on Finite Element Method to Quantify Damage Evolution Due to External Sulfate Attack on Self‐Compacting Concretes

Abstract: This work combines experimental and numerical investigations to study the mechanical degradation of self‐compacting concrete under accelerated aging conditions. Four different experimental treatments are tested among them constant immersion and immersion‐drying protocols allow an efficient external sulfate attack of the material. Significant damage is observed due to interfacial ettringite. A predictive analysis is then adopted to quantify the relationship between ettringite growth and mechanical damage evolution during aging. Typical 3D microstructures representing the cement paste‐aggregate structures are generated using Monte Carlo scheme. These images are converted into a finite element model to predict the mechanical performance under different criteria of damage kinetics. The effect of ettringite is then associated to the development of an interphase of lower mechanical properties. Our results show that the observed time evolution of Young's modulus is best described by a linear increase of the interphase content. Our model results indicate also that the interphase regions grow at maximum stress regions rather than exclusively at interfaces. Finally, constant immersion predicts a rate of damage growth five times lower than that of immersion‐drying protocol.     

The effect of cohesive forces on the fluidization of aeratable powders

The effects of cohesive forces of van der Waals type in the fluidization/defluidization of aeratable type A powders in the Geldart classification are numerically investigated. The effects of friction and particle‐size distribution (PSD) on some design‐significant parameters, such as minimum fluidization and bubbling velocities, are also investigated. For these types of particles, cohesive forces are observed as necessary to fully exhibit the role friction plays in commonly observed phenomena, such as pressure overshoot and hysteresis around minimum fluidization. This study also shows that a full‐experimental PSD consisting of a dozen particle sizes may be sufficiently represented by a few particle diameters. Reducing the number of particle types may benefit the continuum approach, which is based on the kinetic theory of granular flow, by reducing computational expense, while still maintaining the accuracy of the predictions. Published 2013 American Institute of Chemical Engineers AIChE J 60: 473–484, 2014     

Extension of Hill-Koch-Ladd drag correlation over all ranges of Reynolds number and solids volume fraction

Hill et al. [R. J. Hill, D.L. Koch, J.C. Ladd, J. Fluid Mech. (2001), 448, pp. 213-241 and 243-278] proposed a set of drag correlations, based on data from Lattice-Boltzmann simulations. These correlations, while very accurate within the range of void fractions and Reynolds numbers used in the Lattice-Boltzmann simulations, do not cover the full range of void fractions and Reynolds numbers encountered in fluidized bed simulations. In this paper a drag correlation applicable to the full range of void fractions and Reynolds numbers is developed by blending the Hill-Koch-Ladd (HKL) drag correlation with known limiting forms of the gas-solids drag function such that the blended function is continuous with respect to Reynolds number and void fraction. This study also corrects a misinterpretation of the HKL drag correlation that was published in the literature, which makes the drag function discontinuous with respect to the Reynolds number.Two examples of gas/solids flows in a bubbling fluidized bed and a one-dimensional channel flow are used to illustrate differences between the proposed extension of HKL drag correlation and another form published in the literature.     

Synthesis and characterization of Ag nanoparticles–polyaniline composite powder material

The chemical deposition of silver particles in polyaniline (PANI) powder has been carried out via the reduction of Ag⁺ ions by PANI in various concentrations of AgNO₃ aqueous solutions. It is found that the rate of Ag(I) reduction and the size of the metal particles incorporated were strongly dependent on the reaction medium, the PANI redox form and the stirring method used. Homogeneous distribution of silver nanoparticles into PANI matrix was obtained at low Ag(I) concentration, PANI in emeraldine base form and short reaction time under ultrasonic stirring. The presence of silver particles dispersed into porous polyaniline structures was confirmed using X-ray diffraction, scanning electron microscopy and cavity microelectrode (CME) technique in acidic aqueous electrolyte. The electrochemical study of Ag-PANI composite by CME showed that the redox system of silver depends on the size and the distribution of metal particles incorporated into PANI.     

Verification and validation study of some polydisperse kinetic theories

The predictions of several polydisperse kinetic theories are presented in this study for the simple shear flow of a binary mixture of powders with varying sizes in a vacuum under zero gravity. These results are compared to published numerical data obtained using discrete molecular dynamics technique. The theory showing the most accurate results is modified so that the sum of the kinetic stresses of two or more identical solid phases adds to that of a monodisperse system with the same properties. Simulation results obtained in a three-dimensional riser for the flow of air and a binary mixture of glass beads are compared with available experimental data for each solid-phase velocity, concentration, and granular temperature. The predictions of the theory compare reasonably well with experimental data when the value of the linear particle-particle restitution coefficient is lowered to take into account the extra energy dissipation due to collisions between pairs of slightly frictional particles.     

Meso-scale structures of bidisperse mixtures of particles fluidized by a gas

Flow characteristics of bidisperse mixtures of particles fluidized by a gas predicted by the mixture based kinetic theory of [Garzó et al., 2007a] and [Garzó et al., 2007b] and the species based kinetic theory model of Iddir and Arastoopour (2005) are compared. Simulations were carried out in two- and three-dimensional periodic domains. Direct comparison of the meso-scale gas-particle flow structures, and the domain-averaged slip velocities and meso-scale stresses reveals that both mixture and species based kinetic theory models manifest similar predictions for all the size ratios examined in this study. A detailed analysis is presented in which we demonstrate when the species based theory of Iddir and Arastoopour (2005) will reduce to a mathematical form similar to the mixture framework of [Garzó et al., 2007a] and [Garzó et al., 2007b] . We also find that the flow characteristics obtained for bidisperse mixtures are very similar to those obtained for monodisperse systems having the same Sauter mean diameter for the cases examined; however, the domain-averaged properties of monodisperse and bidisperse gas-particle flows do demonstrate quantitative differences. The use of filtered two-fluid models that average over meso-scale flow structures has already been described in the literature; it is clear from the present study that such filtered models are needed for coarse-grid simulations of polydisperse systems as well.