Optimized wideband horn antenna for millimeter-wave spectroscopy applications

In the paper, an influence of antennas transmitting the electromagnetic wave to the sample cell of a millimeter-wave molecular spectrometer on the properties of the whole device is discussed. A conventional rectangular horn antenna is considered as the reference antenna, and a double ridge horn antenna is designed, modeled and optimized in order to improve parameters of the spectrometer potentially. A detailed comparison of the reference antenna and the double ridge horn shows that a wider frequency band can be covered by the designed antenna, but the gain achieved is lower.     

Application of wet effluent diffusion denuder for measurement of uptake coefficient of gaseous pollutants

The comparison of theoretical approaches describing the collection of analyte in the cylindrical wet effluent diffusion denuder (CWEDD) with experimental data is presented. Various absorption liquids were tested for the collection of formaldehyde (distilled-deionized water, H₂SO₄ solution), acetaldehyde (distilled-deionized water) and nitrous acid (distilled-deionized water, sodium carbonate and sodium bicarbonate solutions of various concentrations and sodium phosphate pH 6-8) in CWEDD. pH of absorption liquids significantly influences the collection of formaldehyde as well as nitrous acid. The collection efficiency of formaldehyde for 0.05 M H₂SO₄ as absorption liquid was generally higher than for distilled-deionized water. Absorption liquid pH markedly affected the collection efficiency of HONO too (with increasing pH the collection efficiency increase). Data derived by Gormley-Kennedy equation for all investigated compounds were overestimated especially for higher flow rates of air, data calculated with respect to Henry constant are not in good agreement with experimental data and are considerably depended on a determination of the Henry constant value. The CWEDD can be alternative tool for the determination of uptake coefficient. Obtained uptake coefficients were in good agreement with data found in other literature.     

A metastable Fe(A) termination at the Fe3O4(001) surface

A metastable Fe(A) terminated Fe₃O₄(001) surface was prepared by tailoring the surface preparation conditions. STM, LEIS and LEED are utilized to demonstrate that annealing the Ar⁺ sputtered surface to 350 °C produces an Fe(A) terminated surface with a (√2 × √2)R45° superstructure. Within the superstructure both single Fe atoms and Fe dimer species are observed. The surface is reoxidized upon annealing to higher temperatures, eventually leading to the recovery of the energetically favorable Jahn–Teller distorted surface at 700 °C. The ability to reproducibly prepare the Fe(A) termination in this simple manner will allow investigations into the structure–function relationship for this important technological material.     

Self-crossing Points of a Line Segment Process

This paper is devoted to planar stationary line segment processes. The segments are assumed to be independent, identically distributed, and independent of the locations (reference points). We consider a point process formed by self-crossing points between the line segments. Its asymptotic variance is explicitly expressed for Poisson segment processes. The main result of the paper is the central limit theorem for the number of intersection points in expanding rectangular sampling window. It holds not only for Poisson processes of reference points but also for stationary point processes satisfying certain conditions on absolute regularity (β-mixing) coefficients. The proof is based on the central limit theorem for β-mixing random fields. Approximate confidence intervals for the intensity of intersections can be constructed.     

Empirical distributions in marked point processes

We study the asymptotic behaviour of the empirical distribution function derived from a stationary marked point process when a convex sampling window is expanding without bounds in all directions. We consider a random field model which assumes that the marks and the points are independent and admits dependencies between the marks. The main result is the weak convergence of the empirical process under strong mixing conditions on both independent components of the model. Applying an approximation principle weak convergence can be also shown for appropriately weighted empirical process defined from a stationary d-dimensional germ-grain process with dependent grains.     

Hydrogen Economy and Polymer Membranes

Summary: Hydrogen can be separated from its mixtures using polymer foams with closed cells. Each cell serves as a gas container which is filled through its walls – separation membranes. Foam, as a manifold membrane system, utilizes transient states of permeation and thus takes advantage of fastest diffusion of hydrogen. Large scale manufactured polystyrene foams were chosen to demonstrate the phenomenon. Novel proton conducting membranes containing ionic liquids are being developed. They can perform in intermediate-temperature fuel cells (FC).     

Electrochemical Fluorographane: Hybrid Electrocatalysis of Biomarkers,Hydrogen Evolution,and Oxygen Reduction

Fluorographane (C₁H_xF_1?x+δ)_n is a new member of the graphene family that exhibits hydrophobicity and a large band gap that is tunable based on the level of fluorination. Herein, sensing and energy applications of fluorographane are reported. The results reveal that the carbon‐to‐fluoride ratio of fluorographane has a great impact on the electrochemical performance of the materials. Lowered oxidation potentials for ascorbic and uric acids, in addition to a catalytic effect for hydroquinone and dopamine redox processes, are obtained with a high fluoride content. Moreover, fluorographane, together with residual copper‐ and nickel‐based doping, acted as a hybrid electrocatalyst to promote hydrogen evolution and oxygen reduction reactions with considerably lower onset potentials than those of graphane (starting material), which makes this a promising material for a broad range of applications.     

Optimization of sol–gel/pyrolysis routes to silicon oxycarbide glasses

The optimization of the synthesis of silicon oxycarbide ceramics via the sol–gel/pyrolysis route is described, starting from several alkylalkoxysilanes and vinylalkoxysilanes. The main aim was to achieve low weight losses during cure and pyrolysis and also a compact ceramics morphology. The theoretical composition of the pyrolysates was changed between SiO_1.5C and SiO_1.2C_2.3, by varying monomer types and ratios. An assessment of the real composition was performed using energy-dispersive X-ray spectroscopy. The smallest weight losses were obtained for the resins based on vinyltriethoxysilane and dimethyldiethoxysilane which were additionally modified by the addition of a small amount of boric acid. Somewhat higher weight losses combined with the best toughness were found for resins based on non-vinylated silsesquioxane with a low content on linear dimethylsiloxane units. As an alternative, a precursor (SiO_0.9C_2.8) was prepared via hydrosilylation, based on cyclic dimethylsiloxane oligomers interconnected to a network, but its weight losses were higher than those of sol–gel silicon oxycarbide.