A predictive model based on tortuosity for pressure drop estimation in ‘slim’ and ‘fat’ foams

The use of porous structures with high external surface area represents an important breakthrough in several industrial applications. Foam structures have received an increasing scientific and industrial interest since the last decade. Knowledge of pressure drop induced by these foam structures is thus essential for successful design and operation of high performance industrial systems. In this context, an analytical investigation was conducted for the determination of the permeability and the inertial coefficient in foams. The theoretical model is based on modified cubic lattice, which allows to take into account the presence of matter at the junction of struts. The existing model developed in the literature is then modified to incorporate this geometrical approach for determining the tortuosity of the foam. Finally, the permeability and inertial coefficient analysis are performed in order to derive the pressure drop on foams. The modeling procedure is based only on physical principles and geometrical considerations with no adjustable parameters in order to reconcile the theoretical work with the experimental data of the literature. Finally, this model is validated for two marginal cases (i.e. ‘slim’ and ‘fat’ foams).     

The Characterisation of Pluripotent and Multipotent Stem Cells Using Fourier Transform Infrared Microspectroscopy

Fourier transform infrared (FTIR) microspectroscopy shows potential as a benign, objective and rapid tool to screen pluripotent and multipotent stem cells for clinical use. It offers a new experimental approach that provides a holistic measurement of macromolecular composition such that a signature representing the internal cellular phenotype is obtained. The use of this technique therefore contributes information that is complementary to that acquired by conventional genetic and immunohistochemical methods.     

In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid‐acid‐catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature‐dependent volatile‐product‐slate changes when the polymer was cracked with HZSM‐5 and HY zeolites and the protonated form of MCM‐41. Volatile‐product distributions depended on the catalyst acidity and pore size. With HZSM‐5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30–40°C higher than those required for olefin production. Small olefins (C₃–C₅) were the most abundant products when HZSM‐5 and MCM‐41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C₄–C₈). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM‐5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile‐product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3118–3125, 2001     

In-depth study of the Ruddlesden-Popper LaxSr2−xMnO4±δ family as possible electrode materials for symmetrical SOFC

The Ruddlesden Popper (RP) manganites La_xSr_2?xMnO_4±δ with compositions 0.25 ≤ x ≤ 0.6 have been successfully synthesized as single phases by solid-state reaction in air. All those materials are not only stable in reducing atmosphere but they also maintain the K₂NiF₄-type structure with I4/mmm symmetry under redox cycling conditions with limited volume changes. The x = 0.5 phase was analyzed by in situ high temperature neutron powder diffraction (HTNPD), under flowing hydrogen, showing the formation of oxide-ion vacancies on the equatorial sites of the perovskite planes, during reduction process. The total electrical conductivity was optimized and found maximum for x = 0.5 with values of 35.6 S cm^?1 and 1.9 S cm^?1 at 800 °C in air and 3% H₂/Ar, respectively, what is judged to be sufficient for an active layer of symmetrical SOFC electrode. First Electrochemical Impedance Spectroscopy (EIS) measurements in both oxidizing and reducing conditions, using an YSZ electrolyte and a GDC buffer layer, are presented giving rise to promising values.     

The eddy current model as a low-frequency,high-conductivity asymptotic form of the Maxwell transmission problem

We study the relationship between the Maxwell and eddy current (EC) models for three-dimensional configurations involving bounded regions with high conductivity $\sigma$ in air and with sources placed remotely from the conducting objects, which typically occur in the numerical simulation of eddy current nondestructive testing (ECT) experiments. The underlying Maxwell transmission problem is formulated using boundary integral formulations of PMCHWT type. In this context, we derive and rigorously justify an asymptotic expansion of the Maxwell integral problem with respect to the non-dimensional parameter $\gamma ?\sqrt{\omega {\epsilon }_0∕\sigma }$. The EC integral problem is shown to constitute the limiting form of the Maxwell integral problem as $\gamma \to 0$, i.e. as its low-frequency and high-conductivity limit. Estimates in $\gamma$ are obtained for the solution remainders (in terms of the surface currents, which are the primary unknowns of the PMCHWT problem, and the electromagnetic fields) and the impedance variation measured at the extremities of the excitating coil. In particular, the leading and remainder orders in $\gamma$ of the surface currents are found to depend on the current component (electric or magnetic, charge-free or not). These theoretical results are demonstrated on three-dimensional illustrative numerical examples, where the mathematically established estimates in $\gamma$ are reproduced by the numerical results.     

Occurrence of the <Emphasis Type="Italic">cis</Emphasis>-4,7,10, <Emphasis Type="Italic">trans</Emphasis>-13-22:4 Fatty Acid in the Family Pectinidae (Mollusca: Bivalvia)

The present study aimed to elucidate the effective phylogenetic specificity of distribution of a cis-4,7,10, trans-13-22:4 (22:4(n-9)Δ13trans) among pectinids. For this purpose, we extended the analysis of membrane glycerophospholipids FA composition to 13 species of scallops, covering 11 genera and 7 tribes representatives of the three subfamilies Chlamydinae, Palliolinae and Pectininae and the subgroup Aequipecten. In species belonging to the subfamily Pectininae and the Aequipecten subgroup, 22:4(n-9)Δ13trans was found in substantial amounts, but it was absent in other species belonging to the subfamilies Chlamydinae and Palliolinae. Homologous non-methylene-interrupted (NMI) FA, also hypothesized to differ along phylogenetic lines in bivalves, were totally absent or present only in trace amounts in representatives of the Aequipecten subgroup but ranged from 0.3 to 4.5% of the total FA in Pectinidae, Chlamydinae, and Palliolinae subfamilies. The species-specific occurrence of NMI and 22:4(n-9)Δ13trans FA in membrane lipids of pectinids agrees with the most recent phylogenies based on shell morphology and molecular characteristics. We examined the potential timing of the appearance of 22:4(n-9)Δ13trans in pectinids on a geologic time scale.     

An efficient bio-inspired catalytic tool for hydrogen release at room temperature from a stable borohydride solution

Commercially available open-cell polyurethane foams (OCPUF) have been successively functionalized with bio-inspired polydopamine coating (OCPUF@PDA), and activated with cobalt nanoparticles (OCPUF@PDA@Co). The resulting soft structured catalytic support (S₂CS) has been used as a highly efficient tool for the release of dihydrogen from a commercially available alkaline sodium borohydride solution at room temperature. With a diluted solution containing 0.4 wt% NaBH₄ and 0.4 wt% NaOH, the hydrogen generation rate was of 76.4 ± 3.18 L·h⁻¹·g_cat⁻¹ after stabilization of the catalytic activity. The catalytic tool could be used for 10 runs.     

High thermal conductive β-SiC for selective oxidation of H2S: A new support for exothermal reactions

This study aims at synthesizing a new by substituting 1 atom% Pd²⁺ in ionic state in TiO₂ in the form of Ti_0.99Pd_0.01O_1.99 with oxide-ion vacancy. The catalyst was synthesized by solution combustion method and was characterized by XRD and XPS. The catalytic activity was investigated by performing CO oxidation, hydrocarbon oxidation and NO reduction. A reaction mechanism for CO oxidation by O₂ and NO reduction by CO was proposed. The model based on CO adsorption on Pd²⁺ and dissociative chemisorption of O₂ in the oxide-ion vacancy for CO oxidation reaction fitted the experimental for CO oxidation. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd²⁺, NO chemisorption and dissociation on oxide-ion vacancy fitted the experimental data. The rate parameters obtained from the model indicated that the reactions were much faster over this catalyst compared to other catalysts reported in the literature. The selectivity of N₂, defined as the ratio of the formation of N₂ and formation of N₂ and N₂O, was very high compared to other catalysts and 100% selectivity was reached at temperature of 350 °C and above. As the N₂O + CO reaction is an intermediate reaction for NO + CO reaction, it was also studied as an isolated reaction and the rate of the isolated reaction was less than that of intermediate reaction.