Sequentlal estimarion in exponential-type processes under random initial conditions

In the present paper exponential type random processes which start from random state and/or time are considered. All efficient sequential plans are determined.     

Submicron-scale patterns on ferromagnetic–antiferromagnetic Fe/NiO layers by focused ion beam (FIB) milling

With the aim of studying the magnetic properties of reduced-dimensionality magnetic systems we have patterned 250 nm- and 500 nm-size square elements on Fe/NiO layers by 30 keV Ga⁺ focused ion beam (FIB) milling, varying beam current and pixel dwell time. By high resolution scanning electron microscope (SEM) imaging and atomic force microscopy (AFM) analysis we found that island size decreases from the nominal value by increasing the beam current and features sharpness improves on increasing the dwell time. The top surface of the isolated features has a pronounced edge bending which may be as high as 9 nm with respect to the flat inner area of the island and decreases as dwell time grows. By varying the ion fluence we found that such a shape is related to a surface swelling effect occurring at low ion fluence in the irradiated areas. The swelling-related damage at the edges is expected to influence the magnetic properties of the patterned features.     

Atomic-Scale Structure of Glasses Using High-Energy X-Ray Diffraction

The great potential of high-energy X-ray diffraction to determine fine details in the atomic scale structure is discussed and illustrated with an example of a successful study on GeSe₂ glass.     

Modified methodology for computing interference in LEO satellite environments

Computing interference is very important in satellite networks design in order to assure the electromagnetic compatibility (EMC) with other radiocommunication systems. There are different methods to compute interference in geostationary (GEO) satellite systems including conventional methods using link budget equations and alternate methods such as increase in noise temperature. However, computing interference in low earth orbit (LEO) systems represents a different problem. Due to the special characteristics of this kind of orbits, the elevation angle at any site changes continuously over time, meaning a time dependent change of the propagation path length between an interfering transmitter and an interfered‐with receiver, and of the discrimination provided by the transmitting and/or the receiving antenna. Thus, conventional interference prediction methods developed for fixed links must be adapted to the case of LEO systems. To overcome this problem a mathematical model that characterizes the path length variations by an average value obtained from the probability density function of the varying distance between an interfering transmitter and an interfered‐ with receiver is proposed in this paper. This average path length enables the use of conventional link budget methods to reduce the computation time for the evaluation of interference in LEO satellite environments. Two practical examples show the possible applications of the proposed model. Copyright © 2003 John Wiley & Sons, Ltd.     

Hydrogen production in ultrarich combustion of hydrocarbon fuels in porous media

Rich and ultrarich combustion of methane, ethane, and propane inside inert porous media is studied experimentally and numerically to examine the suitability of the concept for hydrogen production. Temperature, velocities, and chemical products of the combustion waves were recorded experimentally at a range of equivalence ratios from stoichiometry (φ = 1.0) to φ = 2.5, for a filtration velocity of 12 cm/s. Two-temperature numerical model based on comprehensive heat transfer and chemical mechanisms is found to be in a good qualitative agreement with experimental data. Partial oxidation products of methane, ethane, and propane (H₂, CO, and C₂ hydrocarbons) are dominant for ultrarich superadiabatic combustion. The maximum hydrogen yield is close to 50% for all fuels, and carbon monoxide yield is close to 80%.     

Computer-Aided, Single-Specimen Controlled Bending Test for Fracture-Kinetics Measurement in Ceramics

Fracture testing of ceramics by using controlled crack growth is proposed to allow study of crack-kinetics behavior under a given loading history. A computer-aided, real-time data acquisition system improves the quality of crack-growth parameters obtained in a simple, single-specimen bend test. Several ceramic materials were tested in the present study: aluminum nitride as a linear-elastic material; and alumina and yttria-stabilized zirconia, both representative of ceramics with microstructure-dependent nonlinear fracture properties. Ambiguities in the crack-growth diagrams are discussed to show the importance of accounting for crack-growth history in correctly describing nonequilibrium fracture behavior.     

Ortho-para conversion in solid hydrogen,catalyzed by molecular oxygen impurities

Ortho-para conversion in solid hydrogen with small amounts of molecular oxygen as impurity (0.01–0.5%) was studied by NMR in the temperature range 4.2–7 K. The observed conversion rate was substantially greater than that of the natural conversion process in pure solid H₂ and revealed a strong dependence on temperature and the oxygen content in the sample. Obviously, the conversion is catalyzed by the large paramagnetic moments of O₂ impurities. Since the influence of O₂ is of very short range, the overall rate of the catalyzed conversion in the sample is determined by the relative diffusion of ortho-H₂ and the O₂ impurities. The diffusion coefficient was found to obey an Arrhenius behavior D(T)=3(2). 10^–11.exp[96(8)/T] cm²s^–1. This temperature dependence is interpreted in terms of vacancy-particle exchange by quantum tunneling through the intervening barrier.     

Cerium-doped bioactive 45S5 glasses: spectroscopic,redox, bioactivity and biocatalytic properties

The ability of Ce-containing bioactive glasses, based on 45S5 Bioglass^®, to inhibit oxidative stress in terms of reduction in hydrogen peroxide and superoxide (O₂ ^?), by mimicking the catalase and superoxide dismutase activity is reported in this work. The characterization is performed on the powders of pristine glasses and after the soaking in H₂O₂ solutions and simulated body fluid. The glass samples are analysed by XPS, XRD, UV–Vis and FT-IR. The best catalyst activities are obtained for the glass with the highest content of cerium (H_5.3 = 5.3 mol% of CeO₂ in the nominal glass composition), and the best Ce³⁺/Ce⁴⁺ ratio in terms of catalase mimetic activity is found to be a function of H₂O₂ concentration. Moreover, the detailed study of the surface during the mimic enzymatic activity tests shows the formation of a Ca-P-rich layer on the glass surface, where the presence of Ce ions favours the formation of CePO₄. The phosphate in turn inhibits the formation of hydroxyapatite, decreasing the bioactivity of the glass with the highest of CeO₂ in the glass composition. This work shows the effect of Ce³⁺/Ce⁴⁺ ratio towards the catalase mimetic activity and for the first time the superoxide dismutase mimetic activity of Ce-containing 45S5-derived glasses.