Impedance of blocking electrodes having parallel cylindrical pores with distributed radii

The impedance of blocking porous electrodes having parallel cylindrical pores with a lognormal distribution of their radii, identical pore depth and identical pore volume is calculated. Electrodes with size distribution of variable width, defined by different standard deviation (σ) values, are compared. The effect of varying σ is illustrated for the following cases: (i) the number of pores per unit surface (n) varies with σ while the median of the pore radius distribution (r_μ) remains constant; (ii) r_μ varies with σ while n remains constant; (iii) both n and r_μ vary with σ. It is shown that, although the general shape of the impedance plots is similar in all cases, the assumptions concerning n and r_μ have a major effect on the calculated frequency dependence. All impedance plots exhibit porous behaviour at high frequency and capacitive behaviour at low frequency, the transition being smoother for larger σ values. However, the frequency around which the porous-to-capacitive transition occurs depends on the additional assumptions: it increases as σ increases in cases (i) and (ii) but, in accordance with other authors’ calculations, decreases as σ increases for case (iii).     

Tight binding of the antitumor drug ditercalinium to quadruplex DNA

The structural selectivity of the DNA-binding antitumor drug ditercalinium was investigated by competition dialysis with a series of nineteen different DNA substrates. The 7H-pyridocarbazole dimer was found to bind to double-stranded DNA with a preference for GC-rich species but can in addition form stable complexes with triplex and quadruplex structures. The preferential interaction of the drug with four-stranded DNA structures was independently confirmed by electrospray mass spectrometry and a detailed analysis of the binding reaction was performed by surface plasmon resonance (SPR) spectroscopy. The BIAcore SPR study showed that the kinetic parameters for the interaction of ditercalinium with the human telomeric quadruplex sequence are comparable to those measured with a duplex sequence. Slow association and dissociation were observed with both the quadruplex and duplex structures. The newly discovered preferential binding of ditercalinium to the antiparallel quadruplex sequence d(AG(3)[T(2)AG(3)](3)) provides new perspectives for the design of drugs that can bind to human telomeres.     

Zinc-rich powder coatings corrosion in sea water: influence of conductive pigments

The effect of addition of conductive pigments like carbon blacks on the corrosion behavior of zinc-rich powder paints coated steel in artificial sea water was investigated. Open circuit potential measurements were used to characterize the cathodic protection ability and duration. Micro-Raman spectroscopy analysis was performed in order to identify the corrosion products and to follow the penetration of the solution inside the coatings.

Two different effects were pointed out: an increase of the porosity induced by carbon addition and a galvanic action between zinc and carbon pigments. The performance of the powder coatings, strongly improved if the carbon amount is sufficient, was compared to the one reported for solvent-based zinc-rich paints.     

Metal-Oxo Species in P450 Enzymes and Biomimetic Models. Oxo-Hydroxo Tautomerism with Water-Soluble Metalloporphyrins

Oxygenation reactions (hydroxylation, epoxidation, N- or S-oxide formation, etc.) catalyzed by cytochrome P450 enzymes and related biomimetic models involve an electrophilic oxidative species as the active species, namely a high-valent metal-oxo intermediate. Among the different methods to study the oxygenation reactions mediated by high-valent metal-oxo porphyrin complexes, the recent discovery of oxo-hydroxo tautomerism provides a useful tool to investigate the mechanism of O-atom transfer reactions in aqueous media.     

Copolymerization of norbornene with norbornene terminated polystyrene macromonomer in the presence of Ni-based/MAO catalytic systems

Copolymerization of -norbornenyl polystyrene macromonomer (NBE-PS) with norbornene (NBE) using Ni-based catalysts in combination with methylaluminoxane (MAO) was investigated. The nature of the catalyst, the of the polystyrene macromonomer as well as the [NBE-PS]/[NBE] ratio have been shown to be important parameters to obtain graft copolymers with high NBE-PS incorporation (up to 43 wt%). The compatibilization ability of these graft copolymers has been checked for PS/PNBE blends. The length of the grafts was proved not to be an important parameter to consider compatibilization of the PS/PNBE blend.     

Complex Phase Equilibria in Refractories Design and Use

The current applications of phase diagrams and thermodynamic calculations to studies of refractories are reviewed highlighting links to microstructural analyses. Improved understanding of microstructural evolution and chemical corrosion mechanisms has resulted from such work. The limitation of the calculations/diagrams to thermodynamic equilibria has led to imaginative attempts to incorporate some dynamic aspect in them so they are more relevant to practical conditions. These include varying temperature to model a temperature gradient, P _O2 to model atmosphere permeation into a brick, slag/refractory ratio to model slag penetration and altering the slag composition after reaction with the fine matrix phases. The potential future development of such techniques is discussed.     

Equilibrium Shape of Internal Cavities in Ruby and the Effect of Surface Energy Anisotropy on the Equilibrium Shape

Cavities formed in ruby (99.46Al₂O₃·0.54Cr₂O₃) by the healing and annealing of indentation cracks at 1600°C are more equiaxed than similar cavities in sapphire. Surface energies for the observed facet planes (R, S, and A) relative to the surface energy of the basal plane, C , were γ_A/C= 1.00 ± 0.03, γ_R/C= 1.05 ± 0.07, and γ_S/C= 1.02 ± 0.04, with the uncertainty representing 95% confidence limits. Thus, the surface energies of all observed facets were statistically indistinguishable. Unlike sapphire, P-plane facets were not observed. The substantial rounding of the cavities in ruby indicated that portions of the Wulff shape were above the roughening transition temperature. Thus, even though Cr₂O₃ and Al₂O₃ form ideal solutions, Cr³⁺ ions are sufficiently surface active to modify the relative free energy of the surfaces.     

Ground Fault Tests on High-Resistance Grounded 13.8-kV Electrical Distribution System of Modern Large Chemical Plant?II

Actual ground fault tests were conducted to determine the behavior of low-magnitude arcing ground faults in a closed air-filled 13.8-kV terminal chamber. Ground current magnitudes between 10 and 50 A were allowed to flow under various ground fault conditions. The tests that were performed support the value of high-resistance grounding to promote safety and reduce damage to equipment. At higher ground fault current levels the ionization of the air-filled chamber progresses at a rapid rate, and the arc is sustained or phase-to-phase faulting quickly occurs. The lower the ground fault current can be limited the less damage that occurs and the less possibility there is of creating a phase-to-phase fault. The practical consideration appears to be that if ground fault current can be limited to 10 A or less then initial ground faults will either clear themselves or create solid ground paths. This can allow the system to operate until an orderly shutdown procedure can be initiated.     

Liquid back-mixing in packed-bubble column reactors: a state-of-the-art correlation

The extent of liquid back-mixing in gas–liquid concurrent upflow packed-bubble column reactors is quantified in terms of an axial dispersion coefficient or its corresponding dimensionless Péclet number. Effects of reactor operating conditions on the axial dispersion coefficient are not properly accounted for by the available literature correlations, wherein most often the Péclet number is expressed solely in terms of the gas and liquid Reynolds numbers or superficial velocities. Based on the broadest experimental databank (1322 measurements, 11 liquids, four gases, 28 packing materials, 14 columns diameters, Newtonian, non-Newtonian, aqueous, organic, coalescing and non-coalescing liquids, high pressure, bubble and pulsing flow regime conditions), a state-of-the-art liquid axial dispersion coefficient correlation is obtained by combining neural network modeling and dimensional analysis. Thorough qualitative and quantitative analyses of the constructed databank demonstrate the robustness of the proposed correlation to restore the variety of trend variations of liquid Péclet numbers reported in the literature.