Developmental changes in the precedence effect: estimates of minimum audible angle

The precedence effect refers to an auditory phenomenon which occurs when two similar sounds are presented from different locations with a brief delay, and only one sound is heard whose perceived location is dominated by the first source. Although the lagging source si not localized as an independent event, under some conditions, adults are able to extract its directional cues. Developmental studies suggest that this ability changes during the development. However, those studies have used stimulus configurations which minimize the measurement of that ability. In the present study adults were first tested under several conditions, and the one which produced optimal performance was chosen for testing children. Using the minimum audible angle (MAA) task in the azimuthal plane, performance was compared for a single-source condition and two precedence conditions: in lag discrimination the lagging source changed location while the lead remained at midline, and in lead discrimination the reverse occurred. Subjects were 18 months old, 5 years old, and adult. Significant improvements in MAA occurred with an increase in age, especially in the precedence conditions. Within each group, performance was significantly better in single-source condition, followed by the lead and the lag discrimination.     

Repairing NdBCO-HTSC Powder by Electromagnetic Separation

The aim of this work is to demonstrate the possibility of enriching NdBaCO superconducting powders by electromagnetic separation (EMS) into fractions, which differ substantially in their physical, chemical and superconducting properties. Significant differences in the properties of these fractions were seen. The concentrate fraction amounted to an average of 60–70% wt and was characterized by better superconducting properties, while the tail properties were essentially lower, as required for preparation of superconductors. The concentrate is actually an enriched superconducting powder with optimal quality and the tail is a recycle fraction needing additional thermo-chemical treatment. In addition, the possibility of using EMS as an express method for evaluation of powder quality and quick correction of synthesis parameters will be discussed.      

Effect of alkali and alkaline earth metal ion as glass modifiers on the spectroscopic characteristics of Er3+-ion doped lead silicate glasses

The spectroscopic characteristics of Er-doped lead silicate glasses were investigated with respect to the effects of glass modifiers (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) with various optical basicities. Using the absorption spectra of the glasses, the Judd–Ofelt parameters of the glasses were calculated and examined, with an emphasis on the glass emission intensity ratio at 1572 nm. The spectra of the samples at low temperatures were examined, and the Stark splitting of Er3+ was investigated. The McCumber method was used to determine the emission cross sections of glasses. The SPM glass exhibited high values of full width at half maximum (51.24 nm) and the emission cross section at 1572 nm (1.908 × 10⁻²¹ cm²), with potential applications for guiding component design of 1.5-μm fiber lasers and amplifiers.     

Alloying in platinum-based catalysts for gasoline reforming: A general structural proposal

Platinum/alumina catalysts have been used for many years in the process of gasoline octane upgrading normally referred to as reforming. It is now standard industrial practice to add another element to the catalyst, which may be chosen from many parts of the periodic table, and which acts to prolong the life and improve the selectivity of the catalyst. Additives in use include gallium, germanium, iridium, tin, rhenium and chromium. It is proposed that each of these components alloys with the platinum, but in such a way that the exposed surface of the catalyst particles continues to be wholly platinum. The alloying element is enriched in the immediate subsurface layer, and modifies the properties of the catalyst through an electronic interaction.     

Effect of Grain Thermal Expansion Mismatch on Thermal Conductivity of Porous Ceramics

Many ceramics contain microcracks, which are often situated between sintered grains. These microcracks constitute thermal resistances, which may affect heat transfer through the material and its effective thermophysical properties. The thicknesses and the contact areas of the microcracks change with temperature as a result of the thermal expansion mismatch between the grains on opposite sides of the microcracks. This physical mechanism affects changes of the material's thermal conductivity, k , with temperature. The above mechanism usually plays a minor role at atmospheric pressure, where heat may flow via the gas filling the cracks. Hence, the temperature-induced changes of the crack geometry have little effect on heat transfer. However, at low gas pressures, where the heat flow between the grains occurs mainly via the contact areas, the grains' thermal expansion mismatch causes unusual temperature behavior of the material's thermal conductivity observed for several industrial refractories. In this paper, the influence of the above physical mechanism is discussed relative to other heat transfer mechanisms described in the literature. A simple physical model of the thermal expansion of grains bonded by an agent, having different thermal expansion coefficients, is developed. This model allows calculation of the contact area and the average microcrack opening between the grains as functions of the temperature, the characteristic grains sizes and their thermal expansion coefficients, and the permanent crack area. These parameters are evaluated and used to calculate the effective thermal conductivity of ceramic materials containing microcracks that appear as a result of thermal contraction of grains. The calculated thermal conductivity satisfactorily correlates with the experimental data collected for several chrome-magnesite refractories over a wide range of temperatures and gas pressures.     

Dependence of a crack growth path on the elastic moduli of an anisotropic solid

One of the ways to increase the resistance of a structure to catastrophic fracture is to force a main line crack to deviate from its path. For this reason the influence of the elastic moduli of an anisotropic material on crack rotation are studied. In particular a linear elastic problem for a straight Mode I crack, located on a symmetry axis of an orthotropic plane is considered. The strength properties of the material are assumed to be isotropic. Several crack models are considered for studying the direction of a crack growth path. It is shown that a crack modeled as a thin, elongated, elliptical hole leads to more plausible results concerning crack rotation conditions than an ideal cut model. The maximal tensile stresses are taken as a crack growth criterion. It is shown that for a class of orthotropic materials a crack deviates from the straight path just after it starts to grow, even in the conditions of uniaxial normal tension. The problem of the stability of a straight crack path under Mode I loadings is also considered. This problem is reduced to the problem of the fracture direction determination for thin, elongated, elliptical cavities slightly inclined to the initial direction. The conditions of instability are obtained within the framework of the proposed approach. It is shown that for a class of orthotropic materials a straight crack path is unstable in the conditions of uniaxial normal tension. This class of materials is larger than the one for which a crack deviates from the straight crack path just after its start.     

Compensation of birefringence in active elements with a novel Faraday mirror operating at high average power

A decrease in the depolarization ratio by more than one order of magnitude by use of a recently proposed Faraday mirror (FM) in comparison with the traditional FM has been demonstrated experimentally. At a high average laser power, the possibility of an increase in the accuracy of compensation of depolarization in the active element by means of a lambda/4 plate with both the traditional and the novel FM is shown.     

Ethane interaction with Pt-Cr/H-ZSM-5 catalysts,studied by EXAFS

The effect of high temperature ethane treatment on the dispersion and structure of a Pt-Cr/H-ZSM-5 catalyst has been studied by EXAFS and XPS. At the temperature where ethane aromatisation occurs, (T=820 K), redispersion of platinum-chromium particles has been found, reducing the average particle diameter from 12±2 Å to 8±1 Å. The redispersion explains earlier observations that the aromatisation activity of these catalysts increases during initial use.     

Generation of the second harmonic in the space charge limited diode

The generation of second harmonics of voltage and current in a space charge limited diode is considered. An equation for the second harmonic of the field is derived by an iteration procedure and the efficiency of the yield of the second harmonic is calculated.     

Synchronization of two Q-switched lasers with 150 ps jitter

Two Nd:YLF lasers with a pulse duration of about 2 ns have been synchronized. The duration and synchronization of two laser pulses are provided by two pairs of Pockels cells with synchronized voltage pulses. One of the Pockels cells in the first pair ensures Q switching, and the other cuts out a 2 ns pulse from the giant 20 ns pulse. In the second pair, one of the cells, driven by a two-step voltage pulse, forms a giant pulse synchronized with the pulse of the first laser, and the other cell cuts a short pulse out of it. The proposed scheme allows a rather simple and reliable synchronization of two Q-switched lasers with a jitter of 150 ps.