Local modeling of the aerodynamic heating of the blunt body surface in subsonic high-enthalpy air flow. Theory and experiment on a high-frequency plasmatron

The concept of the local similarity of nonequilibrium boundary layers in high-enthalpy gas flows past blunt bodies is briefly described. The technical possibilities of the VGU-4 induction high-frequency plasmatron in modeling the aerodynamic heating of the hypothetical Pre-X (CNES) spacecraft in the vicinity of the stagnation point of a high-enthalpy air flow are presented. The engineering approach to quantitatively reproduce the thermochemical effect of a dissociated air flow on the vehicle surface in the high-heat region of the terrestrial entry trajectory is developed. In this approach the full-scale values of the total enthalpy, the stagnation pressure, and the velocity gradient at the stagnation point near the surface are reproduced in the experiment. The effective coefficients of O and N atom recombination on a silicone carbide (SiC) surface are determined under the conditions similar with those of the peak heating of the Pre-X vehicle surface in the vicinity of the flow stagnation point.     

New Gilman-type lithium cuprate from a copper(II) salt: synthesis and deprotonative cupration of aromatics

Deprotonative cupration of aromatics including heterocycles (anisole, 1,4-dimethoxybenzene, thiophene, furan, 2-fluoropyridine, 2-chloropyridine, 2-bromopyridine, and 2,4-dimethoxypyrimidine) was realized in tetrahydrofuran at room temperature using the Gilman-type amido-cuprate (TMP)₂CuLi in situ prepared from CuCl₂·TMEDA through successive addition of 1 equiv of butyllithium and 2 equiv of LiTMP. The intermediate lithium (hetero)arylcuprates were evidenced by trapping with iodine, allyl bromide, methyl iodide, and benzoyl chlorides, the latter giving the best results. Symmetrical dimers were also prepared from lithium azine and diazine cuprates using nitrobenzene as an oxidative agent.     

Unusual Optical Properties of Mn‐doped ZnO: The Search for a New Red Pigment—A Combined Experimental and Theoretical Study

A pigment of your imagination : A range of polycrystalline solid solutions of a zinc‐rich Zn_x?1Mn_xO system (see figure) have been prepared and studied in terms of their colour, diffuse reflectance spectra, Mn valence state and electronic structure. The intense optical absorption arises from Mn²⁺ doping and is thought to be due to forbidden or partially forbidden transitions between the valence and the conduction band.

     

Redox catalysis versus heterogeneous one-electron catalysis. Mixed reduction of arenes and alkyl halides at specific palladized electrodes

Reduction of aromatic compounds (A) is achieved in the presence of alkyl halides RX (X = I or Br) at Ag–Pd electrodes in organic solvents. Those electrodes allow the one-electron reduction of RX with the selective formation of free radicals R. This new process (heterogeneous one-electron catalysis, H1EC) was used to alkylate in situ arenes. This mode of alkylation leads to re-visit previous results concerning redox catalysis published by Henning Lund when more conventional electrodes (like glassy carbon or mercury) were used and afforded similar results within a totally different potential scale. These preliminary results underline the reactivity differences between the molecular electrode (A⁻) and the almost ideal catalysis process (facile and specific liberation of free alkyl radicals).     

Temperature dependence of the photonic bandgap and the orientational order parameter for a cholesteric photonic crystal

The reflection spectra of a cholesteric photonic crystal have been measured. The experimental spectra are described by a theoretical expression that follows from the analytical solution of the Maxwell equations. The photonic bandgap width Δν has been determined. The photonic bandgap width changes abruptly as the position of the diffraction band changes. The temperature dependence of the relative bandgap width Δν/ν₀ and the order parameter for a photonic crystal are described by Landau’s theory of phase transitions.     

Probing platinum degradation in polymer electrolyte membrane fuel cells by synchrotron X-ray microscopy

Synchrotron-based scanning transmission X-ray spectromicroscopy (STXM) was used to characterize the local chemical environment at and around the platinum particles in the membrane (PTIM) which form in operationally tested (end-of-life, EOL) catalyst coated membranes (CCMs) of polymer electrolyte membrane fuel cells (PEM-FC). The band of metallic Pt particles in operationally tested CCM membranes was imaged using transmission electron microscopy (TEM). The cathode catalyst layer in the beginning-of-life (BOL) CCMs was fabricated using commercially available catalysts created from Pt precursors with and without nitrogen containing ligands. The surface composition of these catalyst powders was measured by X-ray Photoelectron Spectroscopy (XPS). The local chemical environment of the PTIM in EOL CCMs was found to be directly related to the Pt precursor used in CCM fabrication. STXM chemical mapping at the N 1s edge revealed a characteristic spectrum at and around the dendritic Pt particles in CCMs fabricated with nitrogen containing Pt-precursors. This N 1s spectrum was identical to that of the cathode and different from the membrane. For CCM samples fabricated without nitrogen containing Pt-precursors the N 1s spectrum at the Pt particles was indistinguishable from that of the adjacent membrane. We interpret these observations to indicate that nitrogenous ligands in the nitrogen containing precursors, or decomposition product(s) from that source, are transported together with the dissolved Pt from the cathode into the membrane as a result of the catalyst degradation process. This places constraints on possible mechanisms for the PTIM band formation process.     

Pseudomonas aeruginosa attachment on QCM-D sensors: the role of cell and surface hydrophobicities

While biofilms are ubiquitous in nature, the mechanism by which they form is still poorly understood. This study investigated the process by which bacteria deposit and, shortly after, attach irreversibly to surfaces by reorienting to create a stronger interaction, which leads to biofilm formation. A model for attachment of Pseudomonas aeruginosa was developed using a quartz crystal microbalance with dissipation monitoring (QCM-D) technology, along with a fluorescent microscope and camera to monitor kinetics of adherence of the cells over time. In this model, the interaction differs depending on the force that dominates between the viscous, inertial, and elastic loads. P. aeruginosa, grown to the midexponential growth phase (hydrophilic) and stationary phase (hydrophobic) and two different surfaces, silica (SiO(2)) and polyvinylidene fluoride (PVDF), which are hydrophilic and hydrophobic, respectively, were used to test the model. The bacteria deposited on both of the sensor surfaces, though on the silica surface the cells reached a steady state where there was no net increase in deposition of bacteria, while the quantity of cells depositing on the PVDF surface continued to increase until the end of the experiments. The change in frequency and dissipation per cell were both positive for each overtone (n), except when the cells and surface are both hydrophilic. In the model three factors, specifically, viscous, inertial, and elastic loads, contribute to the change in frequency and dissipation at each overtone when a cell deposits on a sensor. On the basis of the model, hydrophobic cells were shown to form an elastic connection to either surface, with an increase of elasticity at higher overtones. At lower overtones, hydrophilic cells depositing on the hydrophobic surface were shown to also be elastic, but as the overtone increases the connection between the cells and sensor becomes more viscoelastic. In the case of hydrophilic cells interacting with the hydrophilic surface, the connection is viscous at each overtone measured. It could be inferred that the transformation of the viscoelasticity of the cell-surface connection is due to changes in the orientation of the cells to the surface, which allow the bacteria to attach irreversibly and begin biofilm formation.     

Experimental simulation of heat transfer in an HF-plasmatron with lengthened segmented discharge channel

Subsonic and supersonic air induction plasma flows in a VGU-4 100 kW plasmatron with segmented water-cooled cylindrical nozzle with the outlet cross-section 40 mm in diameter are investigated experimentally. The enthalpy on the axis of flow is measured in subsonic air jets. The heat fluxes are measured at the stagnation flow point on a cylindrical water-cooled model 50 mm in diameter located in subsonic air and nitrogen jets. The effect of the generator power, nozzle length, and pressure in the plasmatron pressure chamber on the distributions of the heat flux and the pressure at the stagnation point on the surface of cylindrical models 20 mm in diameter with a plane and hemispheric nose is investigated along the axis of underexpanded dissociated air jets.