Electroluminescence AC powder displays based upon ZnS:Tm, Li

The preparation and characterisation of an inorganic blue-emitting alternate-current electrolumenescent (ACEL) cell based upon ZnS:Tm, Li phosphor powder are described. Electroluminescent and photoluminescent spectra clearly show a dominant blue-emission band peaking at 2.6 eV (477 nm) originated from ¹G₄→³H₆ transition. Advantages and drawbacks of the powder-based ACEL cell have been discussed in comparison with a ACEL thin-film based upon a similar material. The near-infra-red band (801 nm, 1.55 eV, ³F₄→³H₆) seen in thin-film structure was significantly suppressed in these types of devices.     

Multi-source shared nearest neighbours for multi-modal image clustering

Shared Nearest Neighbours (SNN) techniques are well known to overcome several shortcomings of traditional clustering approaches, notably high dimensionality and metric limitations. However, previous methods were limited to a single information source whereas such methods appear to be very well suited for heterogeneous data, typically in multi-modal contexts. In this paper, we propose a new technique to accelerate the calculation of shared neighbours and we introduce a new multi-source shared neighbours scheme applied to multi-modal image clustering. We first extend existing SNN-based similarity measures to the case of multiple sources and we introduce an original automatic source selection step when building candidate clusters. The key point is that each resulting cluster is built with its own optimal subset of modalities which improves the robustness to noisy or outlier information sources. We experiment our method in the scope of multi-modal search result clustering, visual search mining and subspace clustering. Experimental results on both synthetic and real data involving different information sources and several datasets show the effectiveness of our method.     

Room temperature direct space-selective growth of gold nanoparticles inside a silica matrix based on a femtosecond laser irradiation

A one-step procedure without heat-treatment was carried out to yield the space-selective growth of gold nanoparticles inside a transparent silica matrix. A silica porous monolith was prepared via a sol-gel route and then post-doped with an aqueous solution of hydrogen tetrachloroaurate (HAuCl₄) as a gold precursor, in the presence of sodium carbonate as an additive. Direct and local precipitation of gold nanoparticles inside the deep volume of the silica matrix was induced by a femtosecond laser irradiation at room temperature. Gold nanoparticles with size of about 50-60 nm were evidenced by absorption spectroscopy and transmission electron microscopy. The additive is assumed to be involved in a photo-electrochemical mechanism including redox reactions, which is necessary to the formation of gold nanoparticles.     

Fast tree-trellis list Viterbi decoding

A list Viterbi algorithm (LVA) finds the n most likely paths in a trellis diagram of a convolutional code. One of the most efficient LVAs is the tree-trellis algorithm of Soong and Huang. We propose a new implementation of this algorithm. Instead of storing the candidate paths in a single list sorted according to the metrics of the paths, we show that it is computationally more efficient to use several unsorted lists, where all paths of the same list have the same metric. For an arbitrary integer bit metric, both the time and space complexity of our implementation are linear in n. Experimental results for a binary symmetric channel and an additive white Gaussian noise channel show that our implementation is much faster than all previous LVAs.     

Annealing effect on properties of transparent and conducting ZnO thin films

This work presents the effect of postdeposition annealing on the structural, electrical and optical properties of undoped ZnO (zinc oxide) thin films, prepared by radio-frequency sputtering method. Two samples, 0.17 and 0.32 µm-thick, were annealed in vacuum from room temperature to 350 °C while another 0.32 µm-thick sample was annealed in air at 300 °C for 1 h. X-ray diffraction analysis revealed that all the films had a c-axis orientation of the wurtzite structure normal to the substrate. Electrical measurements showed that the resistivity of samples annealed in vacuum decreased gradually with the increase of annealing temperature. For the 0.32 µm-thick sample, the gradual decrease of the resistivity was essentially due to a gradual increase in the mobility. On the other hand, the resistivity of the sample annealed in air increased strongly. The average transmission within the visible wavelength region for all films was higher than 80%. The band gap of samples annealed in vacuum increased whereas the band gap of the one annealed in air decreased. The main changes observed in all samples of this study were explained in terms of the effect of oxygen chemisorption and microstructural properties.     

Alfa fiber/polypropylene composites: Influence of fiber extraction method and chemical treatments

Alfa fiber/polypropylene composites were manufactured using twin-screw extrusion. Fibers were extracted using alkaline and steam explosion methods. Three chemical treatments were also applied to the alkaline-extracted fibers: stearic acid (SA), and potassium permanganate dissolved in water (KW) and in acetone (KA). Finally, thermal annealing was applied to the composites. The results indicate that composites with steam-exploded fibers had a significantly higher melt flow index than composites with alkaline-extracted fibers. Moreover, the incorporation of fibers into the matrix increased the Young's modulus, where the optimum results were obtained utilizing the alkaline-extracted fibers. Both extraction methods also significantly decreased the water uptake, especially the steam explosion. The three chemical treatments increased the melt flow index and conversely decreased the tensile strength and Young's modulus. In addition, KW treatment decreased the water uptake. Finally, thermal annealing increased the tensile strength and Young's modulus of composites with SA-treated fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47392.     

First principles investigation of the substitutional doping of Mn in Mg2Ni phase and the electronic structure of Mg3MnNi2 phase

The substitutional doping of Mn in Mg₂Ni phase and the electronic structure of Mg₃MnNi₂ phase have been investigated by first principles density functional theory calculations. The calculation of enthalpy of formation shows that among the four different lattice sites of Mg(6f), Mg(6i), Ni(3b) and Ni(3d) in Mg₂Ni unit cell, the most preferable site of substitution of Mn in Mg₂Ni lattice has been confirmed to be Mg(6i) lattice site. The constructed Mg₉Mn_3Mg(6i)Ni₆ structure by replacing 3 Mg atoms at Mg(6i) lattice sites with 3 Mn atoms in the Mg₂Ni unit cell is less stable. In contrast, the cubic Mg₃MnNi₂ phase that has the same composition as that of Mg₉Mn_3Mg(6i)Ni₆ structure possesses good stability. Analysis of density of states (DOS) indicates that there is a strong hybridization between Mg s, Mg p and Ni d electrons, which is dominant in controlling the structural stability of pure and Mn-doped Mg₂Ni phases. The Mn-substitution in Mg₂Ni unit cell weakens the interaction between Mg s, Mg p and Ni d electrons, especially for Mg₉Mn_3Mg(6i)Ni₆ phase. The cubic Mg₃MnNi₂ phase possesses a strong hybridization between Mn and Mg, Ni atomic orbits under simultaneously retaining the strong bonding among Mg s, Mg p and Ni d electrons. Based on the calculated results, the stability of phases gradually decreases along the sequence pure Mg₂Ni phase > Mg₃MnNi₂ phase > Mn-substitution doped Mg₂Ni phase.     

Application of multi-model control with fuzzy switching to a micro hydro-electrical power plant

Modelling hydraulic turbine generating systems is not an easy task because they are non-linear and uncertain where the operating points are time varying. One way to overcome this problem is to use Takagi–Sugeno (TS) models, which offer the possibility to apply some tools from linear control theory, whereas those models are composed of linear models connected by a fuzzy activation function. This paper presents an approach to model and control a micro hydro power plant considered as a non-linear system using TS fuzzy systems. A TS fuzzy system with local models is used to obtain a global model of the studied plant. Then, to combine efficiency and simplicity of design, PI controllers are synthesised for each considered operating point to be used as conclusion of an electrical load TS Fuzzy controller. The latter ensures the global stability and desired performance despite the change of operating point. The proposed approach (model and controller) is tested on a laboratory prototype, where the obtained results show their efficiency and their capability to ensure good performance despite the non-linear nature of the plant.     

Synthesis of new silica xerogels based on bi-functional 1,3,4-thiadiazole and 1,2,4-triazole adducts

New transparent Silica-based hybrid materials were synthesized by reaction of polymethylhydrosiloxane (PMHS) and organic compounds: 1,3,4-thiadiazole-2,5-diamine (1), 1,3,4-thiadiazole-2,5-dithiol (2) and 1H-1,2,4-triazole-3-thiol (3), in tetrahydrofuran as solvant using hexachloroplatinic acid (H₂PtCl₆.6H₂O) as a catalyst. PMHS was used as a principal network forming agent, it has been cross-linked via hydrosilylation reaction with bi-functional heterocyclic compounds, leading to the formation of colored gels. These later dried (xerogels) were characterized by numerous techniques, including spectroscopy of (FT–IR) and ¹³C and ²⁹Si CP MAS NMR. The xerogels morphology and texture were studied by scanning electron microscopy and Brunauer–Emmet–Teller method. According to N₂-physisorption results, isotherms are classified as type IV with H₂ type hysteresis loop; then, the xerogels are mesoporous materials. The optic and magnetic properties of the obtained materials were studied by UV–VIS and EPR spectroscopies, respectively. This study showed that all materials are paramagnetic semiconductors.