A real-time estimator of electrical parameters for vector controlled induction motor using a reduced order extended Kalman filter

This paper presents an application of the extended Kalman filter (EKF) to the simultaneous on-line estimation of the dq rotor flux components and all the electrical parameters of a vector controlled induction motor. A time-discrete reduced order model structure is deduced and presents a simple and reduced state equation and a scalar output equation. This approach, combined with the use of the rotor reference frame, offers advantages for real-time identification, compared with full order models, because it reduces the computational cost. The proposed new approach requires the measurement of motor speed, stator voltages and currents signals. Simulation and experimental studies presented in this paper highlight the improvements produced by this new approach based on the extended Kalman filter and a new discretization technique, under real operation conditions

Exploratory study of nanoparticle interaction with intraorally formed dental biofilms

Background The development of nanoparticles offers promising potential for improving biofilm management; however, the biofilm itself acts as a diffusion barrier, limiting effective treatment. This study aimed to investigate the adsorption and diffusion of nanoparticles in an intraorally formed biofilm. Methods Bovine enamel specimens (n=24) were mounted on customized maxillary splints and worn intraorally by two subjects for 24 h to allow biofilm formation. Specimens not exposed to the oral cavity served as controls (n=12). Ex vivo, 20 nm gold nanoparticles with a low-charge polymer outer layer were applied to the biofilm for 10 to 30 min, followed by either a single wash, 20 washes with water, or 24 h of water storage. The outer surface and basal layer of the biofilm were analysed using scanning electron microscopy, while cross-sections were examined using transmission electron microscopy. Results After 24 h of intraoral exposure, enamel was covered by a globular-structured pellicle with bacterial adhesion and occasional biofilm formation, more pronounced in subject 2. Both facilitated nanoparticle adsorption, which increased with exposure time and remained detectable after 20 washes. In subject 2, distinctly more nanoparticles persisted after 24 h of water storage. Transmission electron microscopy confirmed outer surface retention without penetration into deeper biofilm layers. Conclusions The diffusion of 20 nm nanoparticles in dental biofilms appears limited, leaving open questions regarding the optimal nanoparticle size for effective biofilm management and their toxicological implications

Mechanical characterization of cellulose aerogels

Due to dwindling fossil resources, biobased cellulose aerogels, whose three-dimensionally structured networks are characterized by nanoscale fibrils, have been of particular interest in recent years. They can be produced by bringing the polymer chains into solution and subsequent regeneration processes and offer the low density and thermal conductivity typical of aerogels. Their bulk properties depend on their nano and microstructure, which is influenced by their manufacturing process [1]. For practical applications of cellulose aerogels, insights into their elastic and inelastic mechanical properties are desired. To the best of our knowledge, the reports in the literature merely describe the stress-strain curves under monotonic uniaxial compressive loading [2] without exploring the inelastic features. This work aims at extending the state of the art knowhow on mechanical characterization of cellulose aerogels within this context. For this purpose, cellulose aerogels having different cellulose concentrations synthesized using ZnCl2 as solvent, salt hydrate routine [3] were subjected to an intensive mechanical characterization. This included quasi static compression and tensile tests, which for the first time allow a detailed characterization of their strain dependent elastic as well as inelastic properties. Furthermore, the results will be illustrated in the context of computational design of their microstructure with already established approaches [4] to better investigate structure property relations in the future. REFERENCES [1] Rege A, Schestakow M, Karadagli I, Ratke L, Itskov M, Micro mechanical modelling of cellulose aerogels from molten salt hydrates, Soft Matter. 12(34),7079-88, 2016. [2] Buchtova N, Pradille C, Bouvard JL, Budtova T, Mechanical properties of cellulose aerogels and cryogels, Soft Matter, 15, 7901-8, 2019. [3] Schestakow M, Karadagli I, Ratke L, Cellulose aerogels prepared from an aqueous zinc chloride salt hydrate melt, Carbohydrate Polymers, 137, 642-9, 2016. [4] Aney S, Rege A, The effect of pore sizes on the elastic behaviour of open porous cellular materials, Mathematics and Mechanics of Solids, 0(0), 2022

Nanostrukturierte Cellulose-Aerogel-Polyesterverbunde

The mechanically stable nature of cellulose makes it potentially suitable for the reinforcement of polymers. In dissolving the initial cellulose in an aqueous zinc chloride salt hydrate melt it is shaped into a desired form, regenerated, washed, and dried in supercritical CO2 to yield Cellulose-Aerogel (CA) sheets. The aerogel offers a three dimensional network of open porous and thus well accessible cellulose fibrils of 7-25 nm in diameter and lengths of several 100 nm. That randomly arranged nano fibrous felt serves as a predefined network that can be infused by a suitable matrix system to achieve Cellulose-Aerogel Reinforced Polymers(CARPs). The air contained in the aerogel is replaced by capillary assisted infusion with an unsaturated polyester resins for the matrix system to give outstanding composite materials. The density of these composites is found to be only slightly above that of the thermoset itself, since only 6-22 vol.% of fiber reinforcement already has an impact. Mechanical testing using impulse excitation, dynamic mechanical analysis, tensile, and 3-point bending reveal significant improvement by multiplication of the Young’s modulus with respect to the reference thermoset. Furthermore, the incorporation of the cellulose network allows for substantially altered deformation mechanisms yielding shear fracture in CARPs and cleavage fracture in CA. Apart from the strong frequence dependency enormous breaking elongations (>20 %) are observed. Digital image correlation is used to follow local deformation and SEM investigations depict the effect of the Cellulose-Aerogel on the strain behaviour of the final composite material. The strong dependency on the strain rate and the inability of necking leads to the conclusion of CARPs being superplastic materials. As a result, the predefined network of high strength cellulose fibrils can very well serve as a renewable fiber reinforcement for polymers (FRP) utilizing its full potential to yield high performance polymer composites

Nanostrukturierte Cellulose-Aerogel-Polyesterverbunde

The mechanically stable nature of cellulose makes it potentially suitable for the reinforcement of polymers. In dissolving the initial cellulose in an aqueous zinc chloride salt hydrate melt it is shaped into a desired form, regenerated, washed, and dried in supercritical CO2 to yield Cellulose-Aerogel (CA) sheets. The aerogel offers a three dimensional network of open porous and thus well accessible cellulose fibrils of 7-25 nm in diameter and lengths of several 100 nm. That randomly arranged nano fibrous felt serves as a predefined network that can be infused by a suitable matrix system to achieve Cellulose-Aerogel Reinforced Polymers(CARPs). The air contained in the aerogel is replaced by capillary assisted infusion with an unsaturated polyester resins for the matrix system to give outstanding composite materials. The density of these composites is found to be only slightly above that of the thermoset itself, since only 6-22 vol.% of fiber reinforcement already has an impact. Mechanical testing using impulse excitation, dynamic mechanical analysis, tensile, and 3-point bending reveal significant improvement by multiplication of the Young’s modulus with respect to the reference thermoset. Furthermore, the incorporation of the cellulose network allows for substantially altered deformation mechanisms yielding shear fracture in CARPs and cleavage fracture in CA. Apart from the strong frequence dependency enormous breaking elongations (>20 %) are observed. Digital image correlation is used to follow local deformation and SEM investigations depict the effect of the Cellulose-Aerogel on the strain behaviour of the final composite material. The strong dependency on the strain rate and the inability of necking leads to the conclusion of CARPs being superplastic materials. As a result, the predefined network of high strength cellulose fibrils can very well serve as a renewable fiber reinforcement for polymers (FRP) utilizing its full potential to yield high performance polymer composites

Cellulose-Silica Aerogel Composites

Cellulose is the most abundant naturally occurring polymer and given this accessibility it is a highly promising resource in sustainable aerogel developments. Silica aerogels are characterized by a low thermal conductivity but still show insufficient mechanical properties like low stiffness and high brittleness. In the view of improving both the thermal properties of cellulose aerogels and the mechanical properties of silica aerogels, hybrids or composites are of a special interest. In that context, our present work deals with the development of cellulose-silica aerogel composites which were prepared using a "one-pot" process. Cellulose was dissolved using a salt hydrate melt based on cheap zinc chloride tetrahydrate and mixed with a silica sol based on tetraethylsilicate. The gelled cellulose-silica samples were regenerated in ethanol, dried with supercritical CO2 and characterized with respect to shrinkage, density, surface area, mechanical and thermal properties as well as micro-structure via SEM. The monolithic cellulose-silica composites are white in colour and apparently homogeneous. On visual examination the composites seem to get more robust, they feel stiffer and are easier to handle compared with the pure silica aerogels. The silica phase was shown to have a reinforcing effect on the cellulose aerogel by effectively increasing its Young's modulus. Furthermore, the resulting composites yield densities the range of 0.10–0.20 g/cm and specific surface areas in between 600 and 1000 m*m/g outlining an excellent combination of both original aerogels

Exploratory study of nanoparticle interaction with intraorally formed dental biofilms

Abstract Background The development of nanoparticles offers promising potential for improving biofilm management; however, the biofilm itself acts as a diffusion barrier, limiting effective treatment. This study aimed to investigate the adsorption and diffusion of nanoparticles in an intraorally formed biofilm. Methods Bovine enamel specimens (n = 24) were mounted on customized maxillary splints and worn intraorally by two subjects for 24 h to allow biofilm formation. Specimens not exposed to the oral cavity served as controls (n = 12). Ex vivo, 20 nm gold nanoparticles with a low-charge polymer outer layer were applied to the biofilm for 10 to 30 min, followed by either a single wash, 20 washes with water, or 24 h of water storage. The outer surface and basal layer of the biofilm were analysed using scanning electron microscopy, while cross-sections were examined using transmission electron microscopy. Results After 24 h of intraoral exposure, enamel was covered by a globular-structured pellicle with bacterial adhesion and occasional biofilm formation, more pronounced in subject 2. Both facilitated nanoparticle adsorption, which increased with exposure time and remained detectable after 20 washes. In subject 2, distinctly more nanoparticles persisted after 24 h of water storage. Transmission electron microscopy confirmed outer surface retention without penetration into deeper biofilm layers. Conclusions The diffusion of 20 nm nanoparticles in dental biofilms appears limited, leaving open questions regarding the optimal nanoparticle size for effective biofilm management and their toxicological implications