Voltammetric and galvanostatic studies of hydrous and anhydrous iridium oxide films

Electrolytically grown hydrous oxide films on iridium wire electrodes have been thermally treated from 473 to 773 K. Anhydrous oxide films formed by this treatment have been subjected to cathodic polarization at the potential of the hydrogen evolution reaction, square-wave pulsing of potential from –0.25 to +1.25 V with respoect to SCE and to anodic galvanostatic polarization in 0.5 mol dm^–3 H₂SO₄. Cathodic pretreatment caused an increase of the voltammetric charge in the oxide formation region while the square-wave pulsing formed a hydrous oxide film whose voltammetric charge was superimposed on the charge of the anhydrous oxide film. Both procedures restored the hydrophilic nature of the electrode/solution interface. Potential-time curves during anodic galvanostatic polarization served as a diagnostic criterion for the stability and the state of the oxide film.     

Two-variable periodic perturbation of kinetic oscillations

Using one of the generic models (CO oxidation on Pt with surface-oxide formation) predicting kinetic oscillations in heterogeneous catalytic reactions, we show that the efficiency of two-variable periodic perturbations with respect to converting natural period-1 oscillations to period-l oscillations at the forcing frequency is remarkably sensitive to the kind of perturbations used. Counter-phase perturbations are much more effective compared to in-phase perturbations. The physics underlying these findings is suggestive of their applicability to many other models and/or real systems exhibiting kinetic oscillations.     

Influence of the Type and Method of Injection of Oxides Admixtures of Rare Earth Elements on Colour and other Properties of Dental Porcelain

A glassceramic material, which can be used in stomatology for production of dentinal layer of the dental crown multilayer coating, was received. In order to colour the material the admixtures of Tb and Ce compounds were used, as well as composite admixture representing a mixture of Ce, Nd and La oxides. It was demonstrated that the admixture of Tb oxide tones the material only when it is used together with Ce oxide. It was found that the more admixtures of rare earth elements oxides are contained in the sample composition, the higher the colour strength of the sintered material is. The wave length for the test samples is in the range of 600～650 nm, which corresponds to the yellow-orange and orange-red spectral range.     

Influence of Ionic Charge on Diffusion in the Surface Layer of Magnesia

The diffusion of ⁵⁷Co isotope on the MgO (100) surface was investigated by the edge-source method. The surface diffusion parameter, αD_sδ, where α is the segregation factor, D_s the surface diffusion coefficient, and δ the thickness of the high-diffusivity layer, was determined over the temperature region 750° to 1250°C. An Arrhenius plot shows a break at ∼1100°C. Below this temperature ionic or localized transport predominates and above it nonlocalized transport seems to predominate. The divalent Co ion diffuses faster than the trivalent Cr ion in the surface layer. The apparent activation energies for the localized surface diffusion of ⁵⁷Co and ⁵⁹Cr are 59±12 and 110±12 kj/mol, respectively.     

Low-temperature phase formation in the SrF2–LaF3 system

Phase formation in the SrF₂–LaF₃ system was studied at temperatures ranging from 300°C to 450°C using nitrate flux. The solubility of LaF₃ in SrF₂ decreases with decreasing temperature. The equilibrium width of the solid solution region Sr_1−xLa_xF_2+x at 400°C, it is 44.6 ± 0.4 mol% LaF₃ (x = 0.446), at 350°C — 38.3 ± 0.7 mol% LaF₃ (x = 0.383), and decreases almost to zero at 300°C.     

Hydrogen effect on the molecular weight distribution of polymers obtained by polymerization of ethylene and α-olefins over supported titanium-magnesium catalysts

Comparative data on the molecular weight distribution of polymers obtained by polymerization of ethylene, propylene and 1-hexene, and copolymerization of ethylene with α-olefins over the titanium-magnesium catalysts (TMC) in the absence and presence of hydrogen are presented. In contrast to the ethylene polymerization, in the cases of propylene and 1-hexene polymerization and copolymerization of ethylene with α-olefins, the hydrogen addition is characterized by noticeable narrowing of the molecular weight distribution (MWD) due to lower contribution of the MWD component with high molecular weight. This result is an evidence of the increased reactivity of TMC active sites producing high molecular weight poly-α-olefins and copolymers of ethylene with α-olefins in the chain transfer reaction with hydrogen. It is suggested that the increased reactivity of these sites in the transfer reaction with hydrogen appears after the 2,1-addition of α-olefin to the growing polymer chain.     

Antibacterial properties of polyaniline derivatives

This work presents a detailed study on the effect of various functional groups both at the ortho position of the aromatic ring and in the amino group of PANI on the antibacterial properties of polymers against gram-positive (Bacillus subtilis) and gram-negative (Pseudomonas aureofaciens) microorganisms. It was found that incorporation of methyl, methoxy, or pentyl groups into the ortho-position of PANI did not increase the antibacterial activity but in most cases causes a significant decrease in the antibacterial properties of functionally substituted polyanilines. At the same time, PANI derivatives modified by incorporation of pentyl groups into the amino group were found to be more efficient antibacterial compounds against both gram-positive and gram-negative microorganisms than the original polymer. It was also found that N-substituted PANI derivatives manifest not only bactericidal but also bacteriostatic properties toward the test microorganisms. Varying the nature and position of the substituent allowed us to conclude that the synthesis of various N-substituted PANI derivatives with a high degree of doping is the most promising approach to PANI modification for application in bacterial growth inhibition.     

Influence of the post-deformation annealing heat treatment on the low-cycle fatigue of NiTi shape memory alloys

Shape memory alloys (SMA) suffer from the same impairing mechanisms experienced during cycling loading by classic alloys. Moreover, SMA fatigue behavior is greatly influenced by thermomechanical cycling through the zone of thermoelastic phase transformation, which is the basis of shape memory and superelasticity effects. Since the fatigue resistance of any material can be improved by an appropriate thermomechanical treatment, in the present work combined differential scanning calorimetry and microhardness testing were used to determine an optimum annealing temperature for the cold-worked Ni-50.1%Ti alloy. The optimization is based on the assumption that latent heat of transformation is proportional to the mechanical work generated by SMA upon heating, while material hardness is related to the yield stress of the material. It is supposed that an optimum trade-off in these two properties guarantees the best dimensional and functional stability of SMA devices. The level and stability of the mechanical work generated by the material during low-cycle fatigue testing are considered criteria for the material performance and thus of the validity of the proposed optimization procedure.     

Using static suffix array in dynamic application: Case of text compression by longest first substitution

Over the last decade, enhanced suffix arrays (ESA) have replaced suffix trees in many applications. Algorithms based on ESAs require less space, while allowing the same time efficiency as those based on suffix trees. However, this is only true when a suffix structure is used as a static index. Suffix trees can be updated faster than suffix arrays, which is a clear advantage in applications that require dynamic indexing. We show that for some dynamic applications a suffix array and the derived LCP-interval tree can be used in such a way that the actual index updates are not necessary. We demonstrate this in the case of grammar text compression with longest first substitution and provide the source code. The proposed algorithm has O(N²)$O(N^2)$ worst case time complexity but runs in O(N)$O(N)$ time in practice.     

Memory leak detection in Plumbr

Platforms with automatic memory management, such as the JVM, are usually considered free of memory leaks. However, memory leaks can happen in such environments, as the garbage collector cannot free objects, which are not used by the application anymore, but are still referenced. Such unused objects can eventually fill up the heap and crash the application. Although this problem has been studied extensively, nevertheless, there are still many rooms for improvement in this area. This paper describes the statistical approach for memory leak detection, as an alternative, along with a commercial tool, Plumbr, which is based on the method. The tool is later analyzed with three case studies of real applications and in the process also analyzes strengths and weaknesses of the statistical approach for memory leak detection. Copyright © 2014 John Wiley & Sons, Ltd.