Simultaneous in situ reflectance and probe beam deflection measurements at solid electrode-aqueous electrolyte interfaces

A method is herein described for performing simultaneous in situ normal incidence reflectance spectroscopy (DeltaR/R, lambda = 633 nm) and probe beam deflection (PBD) measurements at solid electrodes in aqueous electrolytes, while scanning the potential linearly between two prescribed limits. Results obtained for Au in 0.1 M HClO4 and for Pt in both 0.1 M HClO4 and 0.1 M NaOH were found to be in excellent agreement with those reported in the literature for each individual spectroelectrochemical technique under otherwise similar conditions. Data collected for Pt electrodes in CO-saturated 0.1 M HClO4 revealed rather sudden changes in both DeltaR/R and PBD signals in the voltammetric region where the characteristic sharp peak associated with the oxidation of adsorbed CO occurs. This behavior was ascribed, respectively, to oxide formation (DeltaR/R) and to changes in the electrolyte composition in region neighboring the electrode, involving predominantly the acid concentration (PBD). In contrast, CO oxidation on Pt in 0.1 M NaOH yielded a PBD response consistent with formation of solution-phase carbonate via the reaction of the product, CO2, with hydroxyl ion. The exquisite sensitivity of DeltaR/R and PBD to interfacial phenomena was further illustrated using a monolayer of hemin irreversibly adsorbed on glassy carbon surfaces in 0.1 M Na2B4O7 (pH approximately 9.2). For this system, DeltaR/R was found to be proportional to the relative fractions of hemin and its reduced counterpart, while the PBD signal could be correlated with corresponding variations in the electrolyte concentration induced by the surface-bound redox process.     

Recent research advances on the ECBL approach. Part II: interactive buckling of perforated sections

Perforated cold-formed steel sections are often used in civil engineering as structural members for residential buildings and storage racks construction. In the case of buildings the perforations are provided to permit piping and bridging, while for rack systems they allow for simple connections between members. The load bearing capacity of these sections are influenced not only by the local buckling, global buckling and interaction between these two, but also by the reduction of cross-sectional properties due to perforations. Because of the wide variety in the size and configuration of perforations, it is impossible to provide a practical design procedure to calculate the ultimate strength of such a type of sections. The main objective of this paper is to calibrate an effective design width formula for the perforated sections and, using the ECBL approach, to evaluate an equivalent α imperfection factor for European buckling curves, in order to adapt them for sections with different perforation patterns.     

Oxidation of multiwalled carbon nanotubes by nitric acid

The oxidation of MWCNTs in nitric acid was monitored using sample weight, Raman spectrum, solubility, morphology and alignment. The influence of the acid concentration, temperature and oxidation duration on the monitored parameters was assessed. A new method, based on optical microscopy is proposed for the determination of MWCNT solubility in concentrated aqueous-suspensions. The investigations revealed that the solubility is determined not only by the functional groups on the MWCNT, but also by the functionalized amorphous carbon generated during the digestion of the nanotubes. High solubility (20–40 mg/ml) is obtained only after prolonged exposure (24–48 h) in concentrated acid (60%). But in these conditions 60–90% of the MWCNTs are lost. Furthermore the MWCNTs are strongly fragmented and covered by amorphous carbon after 48 h of oxidation. It was found that the solubility correlates well with the area ratio of the G and D bands from the Raman spectrum. SEM examination of the MWCNT films showed extended alignment after 24 h of oxidation.     

Kinetics of polyesterification and models, 3. Kinetics and mechanism of pentaerythritol esterification by long-chain carboxylic acids at technological conditions

Kinetics of the esterification of pentaerythritol by long-chain carboxylic acids (C₇ – C₁₈) has been followed by potentiometric titrimetry. A simplified approach for the estimation of the rate constant values and the rate constants of the consecutive processes was developed according to the previous established kinetic law for similar systems. A computer simulation of the component concentrations variation has been carried out in order to prove the selected kinetic model.     

Statistics of specular points at a randomly rough surface

Statistical parameters are obtained for an ensemble of specular points at a randomly rough Gaussian statistically isotropic surface at normal incidence. The joint probability density functions (PDFs) of specular point heights and total curvatures are derived separately for maxima, minima, and saddle points. The joint PDFs of brightness and surface elevations of specular points of different types are obtained analytically in an explicit form.     

Photofermentative production of hydrogen from organic acids by the purple sulfur bacterium Thiocapsa roseopersicina

A mutant strain of the anaerobic purple sulfur bacterium Thiocapsa roseopersicina, containing only nitrogenase as a functionally active enzyme for H₂ generation was utilized to study the production of H₂ from organic acids (acetate, pyruvate and succinate). Two types of potential substrates for H₂ production, thiosulfate and salts of various organic acids, were compared under photoheterotrophic growth conditions. Thiosulfate proved to be the preferred electron donor for T. roseopersicina; the consumption of organic acids became pronounced only following depletion of the thiosulfate supply. The system is suitable for the generation of H₂ from effluents of heterotrophic dark fermentation processes or waste streams rich in inorganic reduced sulfur compounds and/or simple organic acids.     

Automata-based verification of programs with tree updates

This paper describes a verification framework for Hoare-style pre- and post-conditions of programs manipulating balanced tree-like data structures. Since the considered verification problem is undecidable, we appeal to the standard semi-algorithmic approach in which the user has to provide loop invariants, which are then automatically checked, together with the program pre- and post-conditions. We specify sets of program states, representing tree-like memory configurations, using Tree Automata with Size Constraints (TASC). The main advantage of this new class of tree automata is that they recognise tree languages based on arithmetic reasoning about the lengths of various (possibly all) paths in trees, like, e.g., in AVL trees or red–black trees. TASCs are closed under union, intersection, and complement, and their emptiness problem is decidable. Thus we obtain a class of automata which are an interesting theoretical contribution by itself. Further, we show that, under few restrictions, one can automatically compute the effect of tree-updating program statements on the set of configurations represented by a TASC, which makes TASC a practical verification tool. We tried out our approach on the insertion procedure for red–black trees, for which we verified that the output on an arbitrary balanced red–black tree is also a balanced red–black tree.