Subgraphs of Interest Social Networks for Diffusion Dynamics Prediction

Finding the building blocks of real-world networks contributes to the understanding of their formation process and related dynamical processes, which is related to prediction and control tasks. We explore different types of social networks, demonstrating high structural variability, and aim to extract and see their minimal building blocks, which are able to reproduce supergraph structural and dynamical properties, so as to be appropriate for diffusion prediction for the whole graph on the base of its small subgraph. For this purpose, we determine topological and functional formal criteria and explore sampling techniques. Using the method that provides the best correspondence to both criteria, we explore the building blocks of interest networks. The best sampling method allows one to extract subgraphs of optimal 30 nodes, which reproduce path lengths, clustering, and degree particularities of an initial graph. The extracted subgraphs are different for the considered interest networks, and provide interesting material for the global dynamics exploration on the mesoscale base.     

Part I: A comparative study of bismuth-modified screen-printed electrodes for lead detection

Lead determination was carried out in the frame of the European Union project Biocop (www.biocop.org) using a bismuth-modified screen-printed electrode (Bi-SPE) and the stripping analysis technique. In order to choose a sensitive Bi-SPE for lead detection, an analytical comparative study of electrodes modified by Bi using "in situ", "ex situ" and "bulk" procedures was carried out. On the basis of the results obtained, we confirmed that the "in situ" procedure resulted in better analytical performances with respect to not only "ex situ" but also to "Bi(2)O(3) bulk" modified electrodes, allowing for a linear range of lead ion concentration from 0.5 to 100 μg L(-1) and a detection limit of 0.15 μg L(-1). We demonstrated that, before the Bi film deposition, an oxidative electrochemical pre-treatment of the working electrode could be useful because it eliminates traces of lead in the graphite-ink, as shown with stripping measurements. It also improves the electrochemical performance of the electrodes as demonstrated with Electrochemical Impedance Spectroscopy (EIS) measurements. The influence of different analytical parameters, such as the electrolyte solution composition (acetate buffer, chloridric acid, nitric acid, perchloric acid) and the ionic strength was investigated in order to evaluate how to treat the sample before the analysis. The morphology of prepared "in situ" Bi-SPEs was also characterized by Atomic Force Microscopy (AFM). Finally, the Bi-SPEs were used to determine the concentration of lead ions in tap and commercial water samples obtaining satisfactory values of the recovery percentage (81% and 98%).     

Detailed XPS and UPS studies of the band structure of zinc oxide

The X-ray photoelectron spectra of zinc oxide were measured in a wide range of quantum energies (30–150 and 1253.6 eV). It is shown that the form of the spectrum of the valence O2p-band depends on the energy of the incident quantum. The most probable reason for the change in the form of the O2p-band spectra is an admixture of Zn3d-electrons, which, along with Zn4s-electronst take part in covalent bonding of Zn and O. The dependence of the integral intensity ratio of the O2p-band to the intensity of the Zn3d peak on hv was analyzed, due to which the percent of the admixture of the Zn3d-states in the O2p-band was determined to be 9%. The stoichiometry and the depth of the profile of the concentration ratio were calculated taking into account the fraction of the Zn3d-electrons participating in the bond. Deceased. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 5, pp. 868–876, September-October, 1997.     

Size and aerial density distributions of Ge nanocrystals in a SiO2 layer produced by molecular beam epitaxy and rapid thermal processing

We discuss the distribution of size and aerial density of Ge nanocrystals in a metal-oxide-semiconductor (MOS) memory structure fabricated by molecular beam epitaxy combined with rapid thermal processing; the size and aerial density of Ge nanocrystals are controlled by varying the thickness of the deposited Ge layer and the processing time. Variation of tunnel oxide thickness is demonstrated with the extension of the processing time. The effect of processing time and tunnel oxide thickness on the electrical properties of the MOS structures is investigated by high frequency capacitance–voltage measurements. PACS  61.46.+w; 81.07.-b; 81.07.Bc; 81.07.Ta     

Controlled loading of building blocks into temporary self-assembled scaffolds for directed assembly of organic nanostructures

Using temporary self-assembled scaffolds to preorganize building blocks is a potentially powerful method for the synthesis of organic nanostructures with programmed shapes. We examined the underlying phenomena governing the loading of hydrophobic monomers into lipid bilayer interior and demonstrated successful control of the amount and ratio of loaded monomers. When excess styrene derivatives or acrylates were added to the aqueous solution of unilamellar liposomes made from saturated phospholipids, most loading occurs within the first few hours. Dynamic light scattering and transmission electron microscopy revealed no evidence of aggregation caused by monomers. Bilayers appeared to have a certain capacity for accommodating monomers. The total volume of loaded monomers is independent of monomer structure. X-ray scattering showed the increase in bilayer thickness consistent with loading monomers into bilayer interior. Loading kinetics is inversely proportional to the hydrophobicity and size of monomers. Loading and extraction kinetic data suggest that crossing the polar heads region is the rate limiting step. Consideration of loading kinetics and multiple equilibria are important for achieving reproducible monomer loading. The total amount of monomers loaded into the bilayer can be controlled by the loading time or length of hydrophobic lipid tails. The ratio of loaded monomers can be varied by changing the ratio of monomers used for loading or by the time-controlled replacement of a preloaded monomer. Understanding and controlling the loading of monomers into bilayers contributes to the directed assembly of organic nanostructures.     

Cross-diffusion in a water-in-oil microemulsion loaded with malonic acid or ferroin. Taylor dispersion method for four-component systems

We describe an improved Taylor dispersion method for four-component systems, which we apply to measure the main- and cross-diffusion coefficients in an Aerosol OT water-in-oil microemulsion loaded with one of the reactants of the Belousov-Zhabotinsky (BZ) reaction, water(1)/AOT(2)/R(3)/octane(4) system, where R is malonic acid or ferroin. With [H(2)O]/[AOT] = 11.8 and volume droplet fraction phi d = 0.18, when the microemulsion is below the percolation transition, the cross-diffusion coefficients D(13) and D(23) are large and positive ( D(13)/ D(33) congruent with 14, D(23)/ D(33) congruent with 3) for malonic acid and large and negative for ferroin ( D(13)/ D(33) congruent with -112, D(23)/ D(33) congruent with -30) while coefficients D(31) and D(32) are small and negative for malonic acid ( D(31)/ D(33) congruent with -0.01, D(32)/ D(33) congruent with -0.14) and small and positive for ferroin ( D(31)/ D(33) congruent with 5 x 10(-4), D(32)/ D(33) congruent with 8 x 10(-3)). These data represent the first direct determination of cross-diffusion effects in a pattern-forming system and of the full matrix of diffusion coefficients for a four-component system. The results should provide a basis for modeling pattern formation in the BZ-AOT system.     

On Gold(I) Complexes and Anodic Gold Dissolution in Sulfite–Thiourea Solutions

Processes involving gold(I) complexes were studied in sulfite–thiourea (TU) solutions. It is shown that at pH >5 the complex [\( {\text{AuTU}}_{2}^{ + } \)] undergoes irreversible decomposition followed by deprotonation and formation of a solid phase. From the data of pH in mixed solutions, the equilibrium constants were evaluated: \( {\text{Au}}({\text{SO}}_{3} )_{2}^{3 - } + i{\text{TU}} \rightleftharpoons {\text{Au}}({\text{SO}}_{3} )_{2 - i} {\text{TU}}_{i}^{2i - 3} + i{\text{SO}}_{3}^{2 - } \), log₁₀ β ₁ = ?1.2, log₁₀ β ₂ = ?3.6. Some aspects of the anodic dissolution of gold in mixed sulfite–thiourea solutions are considered. With the help of the carbonate buffer system the change of the anodic current density j _a was studied at high pH; j _a (pH) has a maximum at pH 11.6–11.9 for E _a = 0.3–0.6 V (vs. NHE). At pH > 12.0, the j _a values decrease sharply. Possible mechanisms of anodic gold dissolution, as well as the role of sulfite, are discussed.