The paper provides an analysis of acoustic emission signals recorded with fiber optic sensors during the propagation of ultrasonic waves in a polymer composite material. The fiber optic sensors for acoustic emission w...
The paper provides an analysis of acoustic emission signals recorded with fiber optic sensors during the propagation of ultrasonic waves in a polymer composite material. The fiber optic sensors for acoustic emission were constructed according to the scheme of an adaptive holographic interferometer. Unlike piezoelectric sensors, fiber optic sensors are distributed type sensors. This imposes certain features on the detection of signals in plates in which fiber optic sensors are embedded. It is established that the spectrum of acoustic emission signals differs in different directions of wave propagation. The local maxima of the spectrum are determined by the mode of wave propagation in the plate in different directions and the location of fiber optic sensors.
Polycrystalline and oriented films of barium disilicide (BaSi2) with a thickness of up to 100 nm were formed on silicon (111) substrates by high-temperature (800 ° C) solid-phase (single-stage and two-stage) anne...
Polycrystalline and oriented films of barium disilicide (BaSi2) with a thickness of up to 100 nm were formed on silicon (111) substrates by high-temperature (800 ° C) solid-phase (single-stage and two-stage) annealing. The single phase of barium disilicide films and their semiconductor nature have been proven to be below 1.25 eV according to X-ray and optical spectroscopic methods. Two preferential orientations of the BaSi2 crystallites were detected and their orientation was determined in the films formed by two-stage annealing. According to the calculations of the parameters of the crystal structure of BaSi2 films, a compression of the unit cell volume from 2.7% to 5.13% was found, depending on the cooling time to room temperature. The stability of the films to laser radiation was studied by registering the Raman spectra with a variable power of laser radiation. The maximum power density of the laser beam (3⋅109 W/m2), which does not lead to the beginning of the destruction of these films, was determined.
Composition, electron density and morphology of metal thin-film nanophases were studied by AES, EELS, AFM and conductivity measurements during MBE deposition of Fe and Co on Si(100) and (111), respectively. AES data d...
Composition, electron density and morphology of metal thin-film nanophases were studied by AES, EELS, AFM and conductivity measurements during MBE deposition of Fe and Co on Si(100) and (111), respectively. AES data demonstrated a layer by layer growth of Fe with a segregation of submonolayer coverage of Si at T = 20 °C and, after annealing at T = 250 °C, a fixed and increased value of the Si-to-Fe Auger-peak ratio in the ranges of d = 0.03−0.12 or 1.2 nm and 0.3−0.6 nm, respectively. EELS spectra indicated a redistribution of valence electrons at the Fe/ Si(100) interface at d = 0.03−0.12 nm. With further increase of Fe thickness, EELS spectra showed transitions to Fe nanophases with lowered concentration of valence electrons near d = 0.12−0.3 nm and d = 0.6−1.2 nm. After annealing AFM images showed the relief stability of stepped Si(100) surface in the range of d = 0.03−0.3 nm, the disappearance of the stepped relief type after 0.3 nm and formation ridge-like islands in Fe film at d = 1.2 nm. Auger peak intensity and conductivity versus the thickness for nanophases of Co on Si(111) showed variations of growth mechanism in accordance with variations of interface layer state.
Numerical modelling of smoldering in porous media under natural convection is considered. Smoldering can be defined as a flameless exothermic surface reaction; it is a type of heterogeneous combustion which can propag...
Numerical modelling of smoldering in porous media under natural convection is considered. Smoldering can be defined as a flameless exothermic surface reaction; it is a type of heterogeneous combustion which can propagate in porous media. Peatbogs, landfills and other natural or man-made porous objects can sustain smoldering under natural (or free) convection, when the flow rate of gas passed through the porous object is unknown a priori. In the present work a numerical model is proposed for investigating smoldering in porous media under natural convection. The model is based on the assumption of interacting interpenetrating continua using classical approaches of the theory of filtration combustion and includes equations of state, continuity, momentum conservation and energy for solid and gas phases. Computational results obtained by means of the numerical model in one-dimensional case are compared with the experimental data of the smoldering combustion in polyurethane foam under free convection in the gravity field, which were described in literature. Calculations shows that when simulating both co-current combustion (when the smoldering wave moves upward) and counter-current combustion (when the smoldering wave moves downward), the numerical model can provide a good quantitative agreement with experiment if the parameters of the model are well defined.
Pulsed-laser dry printing of noble-metal microrings with a tunable internal porous structure, which can be revealed via an ion-beam etching post-procedure, was demonstrated. Average size of the pores inside the micror...
Pulsed-laser dry printing of noble-metal microrings with a tunable internal porous structure, which can be revealed via an ion-beam etching post-procedure, was demonstrated. Average size of the pores inside the microrings were shown to be tuned in a wide range by varying the incident pulse energy and a nitrogen doping level controlled in the process of magnetron deposition of the gold film in the appropriate gaseous environment. The fabricated porous microrings were shown to provide many-fold near-field enhancement of incident electromagnetic fields, which was confirmed by mapping of the characteristic Raman band of a nanometer-thick covering layer of Rhodamine 6G molecules and supporting calculations. The proposed laser-printing/ion-beam etching approach is demonstrated to be a unique tool aimed at designing and fabricating multifunctional plasmonic structures and metasurfaces for spectroscopic bioidentification based on surface-enhanced Raman scattering and photoluminescence detection schemes.
Formation of the highly-ordered [Formula: see text]-periodicity 2D compound has been detected in the (Tl, Au)/Si(1 1 1) system as a result of Au deposition onto the Tl/Si(1 1 1) surface, its composition, structure and...
Formation of the highly-ordered [Formula: see text]-periodicity 2D compound has been detected in the (Tl, Au)/Si(1 1 1) system as a result of Au deposition onto the Tl/Si(1 1 1) surface, its composition, structure and electronic properties have been characterized using scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density-functional-theory calculations. On the basis of these data, the structural model of the Tl-Au compound has been proposed, which adopts 12 Tl atoms and 10 Au atoms (in total, 22 atoms) per [Formula: see text] unit cell, i.e. ∼1.71 ML of Tl and ∼1.43 ML of Au (in total, ∼3.14 ML). Qualitatively, the model can be visualized as consisting of truncated-pyramid-like Au clusters with a Tl atom on top, while the other Tl atoms form a double layer around the Au clusters. The (Tl, Au)/Si(1 1 1)[Formula: see text] compound has been found to exhibit pronounced metallic properties at least down to temperatures as low as ∼25 K, which makes it a promising object for studying electrical transport phenomena in the 2D metallic systems.
Magnesium can be used as a new biodegradable material for orthopaedic applications due to its outstanding properties including high biocompatibility, proper mechanical stiffness and biodegradability. Direct laser depo...
Magnesium can be used as a new biodegradable material for orthopaedic applications due to its outstanding properties including high biocompatibility, proper mechanical stiffness and biodegradability. Direct laser deposition (DLD) as a way of biomedical implant production has been used to make bulk pure Mg. Surface morphology, microstructure and mechanical properties of DLD sample have been studied. The relative porosity of DLD Mg sample has been determined.
Numerical modelling of heterogeneous combustion in porous media with phase transitions is considered. To describe the propagation of time-dependent one-dimensional waves of heterogeneous combustion of metal-containing...
Numerical modelling of heterogeneous combustion in porous media with phase transitions is considered. To describe the propagation of time-dependent one-dimensional waves of heterogeneous combustion of metal-containing mixtures, a mathematical model and a numerical method are proposed. The model is based on the assumption of interacting interpenetrating continua using classical approaches of the theory of filtration combustion and includes equations of state, continuity, momentum conservation and energy for each phase. The numerical method is based on a combination of explicit and implicit finite difference schemes. The carried out numerical calculations showed the efficiency of the proposed model and allowed one to detect the concentration of the condensed metal near the front of the combustion wave.
The paper reports the study of photoluminescence (PL) of disc- and elliptical-shaped SiO2 nanoparticles exited by photons with energy lower than silica bandgap. Differences in the PL spectra are found to be associated...
The paper reports the study of photoluminescence (PL) of disc- and elliptical-shaped SiO2 nanoparticles exited by photons with energy lower than silica bandgap. Differences in the PL spectra are found to be associated with the structure of the nanoparticle excitonic states of optical electrons.
A novel computational model based on the finite volume method is proposed for studying processes in heat-evolutional porous media. The developed model is implemented in OpenFOAM software. The problem of one-dimensiona...
A novel computational model based on the finite volume method is proposed for studying processes in heat-evolutional porous media. The developed model is implemented in OpenFOAM software. The problem of one-dimensional time-dependent gas flow through a porous heat-releasing medium is considered for testing the model. The computational results are compared with those obtained by the previously developed numerical procedure based on the finite difference method, and it is found that the performance of the proposed method is better than that of previously developed one.
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