Plasma-sprayed composite coatings with reduced friction coefficient

The study analyses the tribological properties of a composite plasma sprayed with Al₂O₃-3TiO₂ mixed in various proportions with CaF₂, which is known as a solid lubricant. The coatings were plasma-sprayed in air and were tested using a pin-on-disc tribological set-up. The tests enabled to study their wear resistance and determine the coefficient of friction on the basis of friction force obtained in the course of continuous measurement at a set load. Experiments were optimized by the use of the two-level experiment design aimed at finding the optimal content of CaF₂ in the composite. The influence of the spraying parameters on the coefficient of friction, hardness and surface roughness was determined by means of regression analysis. Metallographical studies of the plasma-sprayed composite were conducted with the use of a scanning microscope with an energy dispersion spectrometer (EDS).     

Switched-capacitor biquads based on switched-capacitor transconductance

A switched-capacitor second-order building block based on switched-capacitor transconductance is presented. All types of transfer functions, e.g. lowpass, bandpass, highpass, and bandstop are possible and experimental results are presented.     

News

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Plaster corset--an important part in the surgical treatment of scolioses (author''s transl)

Single postganglionic neurones to hairy skin and hairless skin of the hindleg were investigated on spinal cord heating and spinal cord cooling in chloralose anesthetized cats. 1. Spontaneously active postganglionic neurones which were classified as vasoconstrictor neurones were depressed by spinal cord heating and excited by spinal cord cooling. The overall response to spinal cord cooling was smaller than that to spinal cord heating. 2. Postganglionic neurones to the hairless skin, which had most likely sudomotor function, responded initially to spinal cord heating with a few impulses or not at all. As judged by the skin potentials recorded from the hairless skin the sweat glands were also only weakly activated at the beginning of the heat stimuli. 3. Six silent postganglionic neurones, 3 each to the hairy skin and to the hairless skin, were excited during spinal cord heating. The response of these neurones consisted of a dynamic and a static component and started at the beginning of the heating stimuli with latencies of less than 10S. The neurones could not be excited by any other stimuli and were classified as cutaneous vasodilator neurones. 4. Quantitative analysis of 4 spontaneously active postganglionic (vasoconstrictor) neurones and 3 silent postganglionic (vasodilator) neurones revealed that the threshold of the responses of these neurones to spinal cord heating was 40-42 degrees C (on the dorsal spinal cord) and that the response increase was maximal at the highest temperatures tested (43-44 degrees C).?     

Enhancements of SDR-Based FPGA System for V2X-VLC Communications

This pilot study focuses on a real measurements and enhancements of a software defined radio-based system for vehicle-to everything visible light communication (SDR-V2X-VLC). The presented system is based on a novel adaptive optimization of the feed-forward software defined equalization (FFSDE) methods of the least mean squares (LMS), normalized LMS (NLMS) and QR decomposition-based recursive least squares (QR-RLS) algorithms. Individual parameters of adaptive equalizations are adjusted in real-time to reach the best possible results. Experiments were carried out on a conventional LED Octavia III taillight drafted directly from production line and universal software radio peripherals (USRP) from National Instruments. The transmitting/receiving elements used multistate quadrature amplitude modulation (M-QAM) implemented in LabVIEW programming environment. Experimental results were verified based on bit error ratio (BER), error vector magnitude (EVM) and modulation error ratio (MER). Experimental results of the pilot study unambiguously confirmed the effectiveness of the proposed solution (longer effective communication range, higher immunity to interference, deployment of higher state QAM modulation formats, higher transmission speeds etc.), as the adaptive equalization significantly improved BER, MER and EVM parameters. The best results were achieved using the QR-RLS algorithm. The results measured on deployed QR-RLS algorithm had significantly better Eb/N0 (improved by approx. 20 dB) and BER values (difference by up to two orders of magnitude).     

Timing of ICSI with Respect to Meiotic Spindle Status

The aim of this study was to evaluate the efficiency of using meiotic spindle (MS) visibility and relative position to the polar body (PB) as indicators of oocyte maturation in order to optimize intracytoplasmic sperm injection (ICSI) timing. This was a cohort study of patients younger than 40 years with planned ICSI, the timing of which was determined by MS status, compared with those without MS evaluation. The angle between PB and MS and MS visibility were evaluated by optical microscope with polarizing filter. Oocytes with MS evaluation were fertilized according to MS status either 5–6 h after ovum pick-up (OPU) or 7–8 h after OPU. Oocytes without MS evaluation were all fertilized 5–6 h after OPU. For patients over 35 years visualization of MS influenced pregnancy rate (PR): 182 patients with MS visualization had 32% PR (58/182); while 195 patients without MS visualization had 24% PR (47/195). For patients under 35 years, visualization of MS did not influence PR: 140 patients with MS visualization had 41% PR (58/140), while 162 patients without MS visualization had 41% PR (66/162). Visualization of MS therefore appears to be a useful parameter for assessment of oocyte maturity and ICSI timing for patients older than 35.     

Early Stages of Composite Formation by Oxidation ofLiquid Aluminum Alloys

Microstructure evolution during the early stages in the directed oxidation of molten Al-Mg and Al-Mg-Si alloys was investigated to provide needed insight into the origins of the incubation period and its practical elimination by SiO₂ additions. Oxidation experiments were performed primarily in thermogravimetric balances and microstructures were analyzed by optical and scanning electron microscopy. Continuous heating above the alloy liquidus produces first a thin MgO layer and then a brief rapid growth of a spinel + metal mixture within a temperature range which depends on the alloy Mg content and the heating rate. The initial rapid oxidation terminates abruptly with the formation of a dense spinel layer at the surface, leading to a long incubation period of negligible weight gain. The surface MgO regenerates in this regime, while the metal channels slowly advance upward by dissolution of the dense spinel, eventually reaching the MgO and inducing the formation of composite nodules. These consist initially of spinel + metal upon which the conventional A1₂O₃+ metal growth starts after the Mg in the near-surface alloy is depleted to a critical level. SiO₂ surface additions promote composite nucleation by locally hindering surface passivation, acting as an O source for continued spinel growth, and modifying the local chemistry to facilitate the formation of A1₂O₃.     

Three‐dimensional finite element calculations in acoustic scattering using arbitrarily shaped convex artificial boundaries

We report on a generalization of the Bayliss–Gunzburger–Turkel non‐reflecting boundary conditions to arbitrarily shaped convex artificial boundaries. For elongated scatterers such as submarines, we show that this generalization can improve significantly the computational efficiency of finite element methods applied to the solution of three‐dimensional acoustic scattering problems. Copyright © 2001 John Wiley & Sons, Ltd.