1,720,965 research outputs found
Mechanical effect of static loading on endodontically treated teeth restored with fiber-reinforced posts.
No full textThe aim of this study was to investigate the mechanical behavior of a dental system built up with fiber-reinforced composite (FRC) endodontic posts with different types of fibers and two cements (the first one used with a primer, the second one without it). Six FRC posts were used. Each system was characterized in terms of structural efficiency under external applied loads similar to masticatory forces. An oblique force was applied and stiffness and maximum load data were obtained. The same test was used for the dentine. The systems were analyzed by scanning electron microscope (SEM) to investigate the surface of the post and inner surface of root canal after failure. The mechanical tests showed that load values in dental systems depend on the post material and used cement. The highest load (281 ± 59 N) was observed for the conical glass fiber posts in the cement without primer. There was a 50 and 85% increase in the maximum load for two of the conical posts with glass fibers and a 229% increase for the carbon fiber posts in the cement without primer as compared with the cement with primer. Moreover, almost all the studied systems showed fracture resistances higher than the typical masticatory loads. The microscopic analysis underlined the good adhesion of the second cement at the interfaces between dentine and post. The mechanical tests confirmed that the strength of the dental systems subjected to masticatory loads was strictly related to the bond at the interface post/cement and cement/dentine
Experimental validation of a high-temperature solar box cooker with a solar-salt-based thermal storage unit
No full textScanning electron microscopic analysis of the efficacy of acid etching on cat enamel
No full textThe effect of etching on cat enamel made with 40% orthophosphoric acid for different times was evaluated. Twenty-one cat teeth were selected and randomly divided into three groups of seven teeth each. They were subjected to etching on a circular area of the coronal enamel (diameter = 2 mm) for 30 s (group A), 45 s (group B) and 60 s (group C). The samples obtained were observed by a scanning electron microscope focusing on the border area between etched and unetched enamel, to highlight the differences. The micrographs were subjected to blind assessment of three experienced operators. The groups were statistically assessed with the Wilcoxon test. At 30, 45 and 60 s, the acid attack results only in the formation of an irregular enamel surface and without uncovering and attack of the prismatic organisation. Prismatic areas with preferential interprismatic action could be detected in few samples etched for 60 s. Analysis with ImageJ was also used to quantify the efficacy of acid etching in the conditions used for human enamel, by an evaluation of grey levels. In cat enamel the etching times considered are not as effective as in human enamel for the purpose of adhesion and the presence of a thick prismless layer could explain this result
Influenza del materiale e della geometria sulle caratteristiche fisiche di un nuovo perno endodontico: analisi mediante elementi finiti (ANSYS)
No full textCon il presente lavoro, sono state valutate le caratteristiche di resitenza a flessione e distribuzione degli stress in un perno in fibra di vetro (evolution fiber post-OGNA) sottoposto ad un carico flessorio
Effect of nanoparticles on heat capacity of nanofluids based on molten salts as PCM for thermal energy storage
Full text linkAbstract In this study, different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (selected as phase change material) with nanoparticles using the direct-synthesis method. The thermal properties of the nanofluids obtained were investigated. These nanofluids can be used in concentrating solar plants with a reduction of storage material if an improvement in the specific heat is achieved. The base salt mixture was a NaNO3-KNO3 (60:40 ratio) binary salt. The nanoparticles used were silica (SiO2), alumina (Al2O3), titania (TiO2), and a mix of silica-alumina (SiO2-Al2O3). Three weight fractions were evaluated: 0.5, 1.0, and 1.5 wt.%. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements on thermophysical properties were performed by differential scanning calorimetry analysis and the dispersion of the nanoparticles was analyzed by scanning electron microscopy (SEM). The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of 15% to 57% in the solid phase and of 1% to 22% in the liquid phase. In particular, this research shows that the addition of silica-alumina nanoparticles has a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. These results deviated from the predictions of the theoretical model used. SEM suggests a greater interaction between these nanoparticles and the salt.The authors would like to thank the Italian National Agency for New Technologies, Energy and Sustainable Economic Development for the financial support of this research.Peer Reviewe
Recent advances in endodontic irrigation: FESEM analysis
No full textOBJECTIVES. The aim of this work is to evaluate the cleansing properties of four different root canal irrigants in extracted dental elements, using the scanning electron microscope (Field Emission Scanning Electron Microscope, FESEM). MATERIALS AND METHODS. Twenty single-rooted dental elements, extracted for periodontal reasons, were subjected to biomechanical bore and canal irrigation through four different tested solutions, namely: irrigant 1 sodium hypochlorite (NaOCl) at 5%; irrigant 2, cetrimide + chlorhexidine (Cetrexidin, Gaba Vebas, Rome, Italy); irrigant 3, ethylenediaminetetraacetic acid (EDTA); irrigant 4, doxycycline + citric acid + polypropylene glycol (Tetraclean, Ogna Laboratori Farmaceutici, Muggi', MB, Italy). All the samples, after proper dehydration and metallization, were observed through the FESEM (SupraTM, Carl Zeiss Microscopy GmbH, Jena, DE) to evaluate the cleansing level achieved in the middle and apical thirds of the canal. RESULTS. The results of our study showed that the irrigant 2 had an excellent cleansing power in the middle third of the canal, although less effective in the apical third. The cleansing power of irrigants 1 and 3 proved to be good enough in the middle third of the canal, although lower than irrigant 2; modest was the cleansing power in the apical third, with special regard to smear-layer removal. Irrigant 4 didn't show any good cleansing capacity, neither in the middle third, nor in the apical third of the canal. CONCLUSIONS. The irrigation practice seems to play a key role in the success of the canal therapy. However, it is not recommendable to use one only irrigating solution in the course of an endodontic treatment. Consequently, using more irrigating solutions at the same time, each with a specific role in endodontic cleansing, seems to be the only viable way to achieve a successful treatment outcome
Analisi e caratterizzazione strutturale e funzionale di perni endodontici fibrorinforzati - Poster Congresso dell’Università degli Studi di Napoli Federico II e Centro di Ricerca Interdisciplinare sui Biomateriali
No full textScopo del lavoro è stato di eseguire una valutazione comparativa tra i perni in fibra Evolution Fiber Post e MicroPost mediante un'analisi agli elementi finiti (ANSYS) e, in aggiunta, mediante forze applicate con dinamometro. Sono state simulate prove di flessione e di compressione
Nanofluids with Enhanced Heat Transfer Properties for Thermal Energy Storage
No full textThis chapter describes recent progress on the development of suspensions of nanometer-sized solid particles in base liquids (nanofluids) for thermal energy storage application.
Among the various methods of energy storage, Latent Heat Thermal Energy Storage (LHTES) Systems using Phase Change Materials (PCMs) have been gaining importance in many fields like solar energy systems, heating and cooling systems and buildings due to their high energy storage density and their ability to provide heat at a constant temperature.
The storage systems utilizing PCMs can be reduced in size respect to systems based on sensible heat. The increase of the thermal capacity of a storage media may allow several advantages for the thermal energy storage systems since a high quantity of heat can be stored in a small volume of material. In this way the thermal storage systems become more compact reducing the overall costs.
Research on nanofluids specific heat has been, however, limited compared to that on thermal conductivity while the description and the analysis of the heat capacity of nanofluids are in fact crucial since its improvement can reduce the amount of storage material.
The chapter starts with a comprehensive description of the principal methods of nanofluid preparation and then it reports the experimental results focusing on the thermal properties with particular attention on the heat capacity enhancement and thermal storage capability as well as the heat of fusion and the characteristic melting temperatures.
Nanofluids based on salts (e.g. nitrates and carbonates) as phase change materials are considered since in the last years several works reported results of nanofluids properties based on mixed salts with different ratio with the addition of different nanoparticles (e.g. oxide nanoparticles, nanotubes). This chapter proposes an overview on the heat capacity enhancement of these nanofluids with the comparison of both theoretical models and experimental results.
Finally, the challenges of using nanofluids in solar energy devices are discussed
ENEA research and innovation on thermal energy storage for CSP plants
No full textThermal Energy Storage is a key factor for efficiency, dispatchability and economic sustainability of Concentrating Solar Power plants. Since 2001 ENEA has developed new CSP plants concepts using molten salts as heat transfer fluid, in which TES is a crucial component. Starting from its experience, to reduce the cost of solar energy, ENEA has been continuing to study innovative solutions for TES systems, increasing energy density, reducing volumes and costs, and maintaining a high heat exchange efficiency. The storage cost reduction, together with the solar field cost decrease, would make the CSP energy competitive compared to fossil sources. The study of new storage materials and new and efficient solutions for heat exchange are the basis of today research. Two different TES concepts have being developed: the first one is based on particular concretes used as sensible heat storage medium. The second one envisages new types of latent heat TESs in which the phase change materials can be mixed with a small amount of nanoparticles to increase their thermo-physical characteristics. First results are very interesting for energy storage amount, charging/discharging times and cyclability, and permit, in a short-medium time perspective, to develop modular TESs concepts. In a long time perspective, ENEA aims to set up a new research topic on thermochemical storage systems to increase energy density and storage period. This allow the realization of TES with large thermal capacity and seasonal utilization avoiding plants oversizing or fossil thermal backups, contributing to solar plant cost reduction and green-energy amount increasing
A New Phase Change Material Based on Potassium Nitrate with Silica and Alumina Nanoparticles for Thermal Energy Storage
No full textIn this study different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (KNO3 selected as phase change material) with nanoparticles using the direct synthesis method. The thermal properties of the nanofluids obtained were investigated. Following the improvement in the specific heat achieved, these nanofluids can be used in concentrating solar plants with a reduction of storage material. The nanoparticles used (1.0 wt.%) were silica (SiO2), alumina (Al2O3), and a mix of silica-alumina (SiO2-Al2O3) with an average diameter of 7, 13, and 2-200 nm respectively. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements of the thermophysical properties were performed by DSC analysis, and the dispersion of the nanoparticles was analyzed by SEM microscopy. The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of about 5-10 % in solid phase and of 6 % in liquid phase. In particular, this research shows that the addition of silica nanoparticles has significant potential for enhancing the thermal storage characteristics of KNO3. The phase-change temperature of potassium nitrate was lowered up to 3 °C, and the latent heat was increased to 12 % with the addition of silica nanoparticles. These results deviated from the predictions of theoretical simple mixing model used. The stored heat as a function of temperature was evaluated for the base salt, and the nanofluids and the maximum values obtained were 229, 234, 242, and 266 J/g respectively. The maximum total gain (16 %) due to the introduction of the nanoparticles (calculated as the ratio between the total stored heat of the nanofluids and the base salt in the range of temperatures 260-390 °C) was also recorded with the introduction of silica. SEM and EDX analysis showed the presence of aggregates in all nanofluids: with silica nanoparticles they were homogenously present while with alumina and silica-alumina also zones with pure salt could be detected
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