Photo-induced changes in the optical properties of amorphous As-Ge-S thin films

Changes in the transmission, absorption edge and refractive coefficient in the UV-VIS and the transmission in the IR spectrum of thin As-Ge-S films after irradiation with an argon laser with =488 nm were studied. X-ray microanalysis showed that the composition of the films (with small variations) corresponded to that of the initial substances. Films with a defined concentration of the elements could also be deposited by evaporation of As₂S₃ and GeS₂ from two sources. The optical properties of thin films prepared by thermal evaporation, flash evaporation and coevaporation from two crucibles have been compared. It was found that depending on the component content, both photodarkening and photobleaching coatings in a wide region of can be obtained in thin As-Ge-S films. The results have been explained from the viewpoint of the photostructural changes in chalcogenide layers.     

μ-Synthesis and Hardware-in-the-loop Simulation of Miniature Helicopter Control System

The aim of this paper is to describe in detail the μ-synthesis of a miniature helicopter integral attitude controller of high order and to present results from the hardware-in-the-loop simulation of this controller implementing Digital Signal Processor. The μ-controller designed allows to suppress efficiently wind disturbances in the presence of 25 % input multiplicative uncertainty. A simple position controller is added to ensure tracking of the desired trajectory in 3D space. The results from hardware-in-the-loop simulation are close to the results from double-precision simulation of helicopter control system in Simulink^®. The software platform developed allows to implement easily different sensors, servoactuators and control laws and to investigate the closed-loop system behavior in presence of different disturbances and parameter variations.     

Measuring Energy Releases in a Scintillation Detector and the Afterpulses of the Photomultiplier Tubes

A procedure for measuring energy releases in scintillation detectors by using a logarithmic RC converter in combination with a device that suppresses photomultiplier tube afterpulses is described. The total range of measured energies is 5.8 MeV to 11.6 GeV. The afterpulse suppression ratio is more than 200. The output pulse of the RC converter is synchronized with the leading edge of the anode signal from the photomultiplier tube.__________Translated from Pribory i Tekhnika Eksperimenta, No. 4, 2005, pp. 26–33.Original Russian Text Copyright © 2005 by V. Volchenko, G. Volchenko, Dzaparova, Karpov, Petkov, Yanin.     

Lubrication of Silicon Nitride and Silicon Carbide by Water: Running in,Wear and Operation of Sliding Bearings

The purpose of this work was to establish the conditions for the operation and break-in of water-lubricated ceramic bearings. The experiments consisted of sliding 1/4 silicon nitride or—carbide balls against pre-polished disks of the same material in water until tribochemical wear generates smooth conformal surfaces that allow hydrodynamic lubrication (<0.002) by very thin water films. This running in was performed at various sliding speeds (0.01-4m/s) and loads (0.5-20N). The minimum sliding speed for low friction were 0.04m/s for silicon nitride and 0.5m/s for silicon carbide, much lower than for conventional bearings. The load carrying pressures were 60-80MPa, which is higher than the usually pressures of thrust bearings. The hydrodynamic fluid film thickness was estimated with a standard integration of Reynolds' equations modified for circular geometry, it was to be 5-15nm for silicon nitride, 25nm for silicon carbide. Operation over long distances (80km) allowed us to measure the wear rate during hydrodynamic lubrication; this was found to be <2×10^–11mm³/nm, a rate acceptable for industrial application. A novel method completed during this work allows the determination of the wear rate during run-in. It varies with sliding velocity for silicon nitride, from 1 to 6×10^–5mm³/nm; it is constant at 4×10^–6mm³/nm for silicon carbide.     

Inhibition-augmented trainable COSFIRE filters for keypoint detection and object recognition

The shape and meaning of an object can radically change with the addition of one or more contour parts. For instance, a T-junction can become a crossover. We extend the COSFIRE trainable filter approach which uses a positive prototype pattern for configuration by adding a set of negative prototype patterns. The configured filter responds to patterns that are similar to the positive prototype but not to any of the negative prototypes. The configuration of such a filter comprises selecting given channels of a bank of Gabor filters that provide excitatory or inhibitory input and determining certain blur and shift parameters. We compute the response of such a filter as the excitatory input minus a fraction of the maximum of inhibitory inputs. We use three applications to demonstrate the effectiveness of inhibition: the exclusive detection of vascular bifurcations (i.e., without crossovers) in retinal fundus images (DRIVE data set), the recognition of architectural and electrical symbols (GREC’11 data set) and the recognition of handwritten digits (MNIST data set).     

Thermosensitive networks based on high molecular weight polyoxyethylene and N-isopropylacrylamide

Summary γ- and UV-irradiation was successfully used for the preparation of mixed networks on the basis of high molecular weight polyoxyethylene (POE) and/or N-isopropylacrylamide and poly(N-isopropylacrylamide) (PNIPAAm). These gels preserve the swelling transition temperature of the pure PNIPAAm and shrink faster above this temperature due to the hydrophilic POE chains. It was found that in a collapsed state these gels retain alkaline organic salts from aqueous solutions. Received: 12 February 1999/Revised version: 18 May 1999/Accepted: 18 May 1999     

On the bottom summation

We consider summation of consecutive values (φ(v), φ(v + 1), ..., φ(w) of a meromorphic function φ(z), where v, w ∈ ℤ. We assume that φ(z) satisfies a linear difference equation L(y) = 0 with polynomial coefficients, and that a summing operator for L exists (such an operator can be found—if it exists—by the Accurate Summation algorithm, or, alternatively, by Gosper’s algorithm when ordL = 1). The notion of bottom summation which covers the case where φ(z) has poles in ℤ is introduced. The text was submitted by the authors in English.     

Iron oxide nanoparticles supported on mesoporous MgO and CeO2: A comparative physicochemical and catalytic study

Iron (III) containing nanoparticles with superparamagnetic behaviour are prepared via deposition on various mesoporous supports (MgO, CeO₂ and SBA-15). XRD, TEM-EDX, N₂ physisorption, FTIR, and Moessbauer spectroscopy are used for their characterization. The reductive properties and catalytic behaviour in methanol decomposition of the materials are also studied. Depending on the chemical nature of the support, the predominant formation of: isolated iron species, strongly interacting with the support (for SBA-15), mixture of hematite and binary MgFe₂O₄ nanoparticles (for MgO) or almost homogeneously dispersed hematite particles (for CeO₂) are observed. The state of iron species strongly affects their catalytic properties. The favorable effect of the support mesoporosity on the catalytic activity is most pronounced for the iron modified CeO₂.