Potential applications of LF-noise spectroscopy to the development of new-generation gas sensors

The solution proposed relates to flicker-noise gas sensors under development, which differ from conventional chemical sensors in offering exceptional selectivity for the analysis of a gaseous environment. The classification and analytical justification are given of low-frequency-noise spectroscopy techniques and measures that are proposed for investigation of disordered semiconductors. The feasibility is shown of patterning processes for flicker-noise gas sensors. Some methods are proposed for these processes and for measurement procedures of gaseous-environment monitoring.     

AlGaN-based quantum-well heterostructures for deep ultraviolet light-emitting diodes grown by submonolayer discrete plasma-assisted molecular-beam epitaxy

Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al _x Ga_{1 ? x} N/Al _y Ga_{1 ? y} N quantum wells. Structural and optical properties of the Al _x Ga_{1 ? x} N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al₂O₃ substrates, heterostructures for light-emitting diodes with Al _x Ga_{1 ? x} N/Al _y Ga_{1 ? y} N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm.     

Effect of hot pressing on processing and properties of BBN ceramics

BBN (BaBi₂Nb₂O₉) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators.     

Novel electro-optic properties of epitaxially grown (Pb, La)(Zr, Ti)O3 (PLZT) thin films derived by advanced sol–gel methods

Advanced sol–gel methods using a secondary solvent addition into (Pb, La)(Zr, Ti)O₃ (PLZT) sol–gel solution and a methanol pre-treatment of sapphire substrates are demonstrated. For the secondary solvent addition, the additive affected the crystallinity and electro-optic (EO) property of PLZT films and only methanol addition can improve them. In addition, the methanol pre-treatment is also appeared to be effective to improve film characteristics.

Through these optimizations, epitaxially grown PLZT thin films on r-cut sapphire are obtained and a high Pockels coefficient which is comparable to those of bulk PLZTs is achieved. It is believed that these PLZT thin films are applicable for integrated EO devices and open the door for the future data communication systems.     

Photo-Fenton removal of water-soluble polymers

This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), were tested under different conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based on the evolution of the TOC–time curves. Under specific reaction conditions, the formation and coalescence of solid particles was visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be coupled with solid separation systems, which may reduce the treatment cost.     

Swift and Selective Reduction of Nitroaromatics to Aromatic Amines with Ni–Boride–Silica Catalysts System at Low Temperature

Various nitroaromatics are successfully reduced to amines with 100% conversion and selectivity in methanol at low temperature (≈5 °C), by using versatile system of 5% Ni–SiO₂ catalyst and NaBH₄ and in situ generation of Ni boride. The catalytic efficiency of Ni loading (5%, 10% and 15%) with silica or titania as support materials is investigated for reduction of nitrobenzene. The Ni–titania/NaBH₄ system recorded lower conversion and selectivity. The IR studies indicate that silica support does not have free –OH group on its surface. Thus the nickel boride is anchored to the silica to facilitate the catalytic process.     

Dynamic response and behavior of reinforced concrete slabs under impact loading

Reinforced concrete slabs are among the most common structural elements. In spite of the large number of slabs designed and built, the effect of their details on their behavior under impact loads are not always appreciated or properly taken into account. This experimental study was aimed at understanding the dynamic behavior of structural concrete slabs under impact loading to improve the state of the art of protective design. This study investigated the effects of different types of slab reinforcements and the applied impact loads on the dynamic response and behavior of reinforced concrete slabs.     

Prices are macro-observables! Stylized facts from evolutionary finance

Prices are macro-observables of a financial market that result from the trading actions of a huge number of individual investors. Major stylized facts of empirical asset returns concern (i) non-Gaussian distribution of empirical asset returns and (ii) volatility clustering, i.e., the slow decay of auto- correlations of absolute returns. We propose a model for the aggregate dynamics of the market which is generated by the coupling of a ‘slow’ and a ‘fast’ dynamical component, where the ‘fast’ component can be seen as a perturbation of the ‘slow’ one. Statistical properties of price changes in this model are estimated by simulation; sample size is 4 × 10⁶. It is shown that increasing the decoupling of these two dynamical levels generates a crossover in the distribution of log returns from a concave Gaussian-like distribution to a convex, truncated Levy-like one. For a sufficiently large degree of dynamic decoupling, the return trails exhibit pronounced volatility clustering.     

Studies on turbulent momentum, heat and species transport during binary alloy solidification in a top-cooled rectangular cavity

A two-dimensional transient fixed-grid enthalpy-based numerical method is developed to analyze the effects of turbulent transport during a binary alloy solidification process. Turbulence effects are introduced through standard k-ε equations, where coefficients are appropriately modified to account for phase-change. Microscopically-consistent estimates are made regarding temperature-solute coupling in a non-equilibrium solidification situation. The model is tested against laboratory experiments performed using an NH₄Cl-H₂O system in a rectangular cavity cooled and solidified from the top. Particular emphasis is laid on studying the interaction between Rayleigh-Benard type convection and directional solidification in the presence of turbulent transport. Numerical predictions are subsequently compared with experimental results regarding flow patterns, interface growth and evolution of the temperature field, and the agreement is found to be good.