1,721,039 research outputs found
A simple approach for upconversion determination using low excitation power: The photoluminescence analysis of an Er-doped aluminosilicate glass
No full textMaterials other than silica can offer better performance in terms of Er solubility and band broadness for integrated Er-doped optical amplifiers and a deep knowledge of their optical properties is therefore fundamental. In this work we describe a simple approach for evaluating upconversion with low pump power excitation, when the standard methods are not very accurate. This is based on the solution of an analytic model which allows the calculation of the 1540nm (I-13/2 --> I-15/2) and the 980nm (I-11/2 --> I-15/2) photoluminescence emissions by considering three energy levels for Erbium.The proposed model has been applied to analyze the luminescence properties of an Er-doped aluminosilicate glass. Firstly some of the system parameters have been evaluated in relation with the lifetimes and with the absorption cross section at 488 nm excitation wavelength. Then the model has been calibrated by comparing the calculated relation between the 980 nm and the 1540 nm emission intensities with the corresponding experimental measurements. This procedure allowed for the determination of the coefficient of cooperative upconversion using pump powers in the range 4-32 mW. An experimental check of the goodness of the method is also presented. (C) 2003 Elsevier B.V. All rights reserved
Yeast lipids from cardoon stalks, stranded driftwood and olive tree pruning residues as possible extra sources of oils for producing biofuels and biochemicals
No full textBackground: Some lignocellulosic biomass feedstocks occur in Mediterranean Countries. They are still largely unexploited and cause considerable problems due to the lack of cost-effective harvesting, storage and disposal technologies. Recent studies found that some basidiomycetous yeasts are able to accumulate high amount of intracellular lipids for biorefinery processes (i.e., biofuels and biochemicals). Accordingly, the above biomass feedstocks could be used as carbon sources (after their pre-treatment and hydrolysis) for lipid accumulation by oleaginous yeasts. Results: Cardoon stalks, stranded driftwood and olive tree pruning residues were pre-treated with steam-explosion and enzymatic hydrolysis for releasing free mono- and oligosaccharides. Lipid accumulation tests were performed at two temperatures (20 and 25 °C) using Leucosporidium creatinivorum DBVPG 4794, Naganishia adeliensis DBVPG 5195 and Solicoccozyma terricola DBVPG 5870. S. terricola grown on cardoon stalks at 20 °C exhibited the highest lipid production (13.20 g/l), a lipid yield (28.95%) close to the maximum theoretical value and a lipid composition similar to that found in palm oil. On the contrary, N. adeliensis grown on stranded driftwood and olive tree pruning residues exhibited a lipid composition similar to those of olive and almonds oils. A predictive evaluation of the physical properties of the potential biodiesel obtainable by lipids produced by tested yeast strains has been reported and discussed. Conclusions: Lipids produced by some basidiomycetous yeasts grown on Mediterranean lignocellulosic biomass feedstocks could be used as supplementary sources of oils for producing biofuels and biochemicals. © 2018 The Author(s)
An outlook on the potential of Si nanocrystals as luminescent probes for bioimaging
No full textSilicon nanocrystals (Si-nc) present several plus points as advanced fluorescent biomarkers but suffer from difficulties met in controlling their intrinsic photoluminescence (PL). Here, we first consider the reasons for this difficulty, showing results that support an interface defect-related origin of the PL. Attainment of a controlled PL emission would then require tuning of defects in the capping oxide, a hard and yet unaddressed task. Alternatively, we demonstrate the possible use of Si-nc as antennas, or sensitizers, of a luminescent rare-earth ion in an engineered fluorophore. In this approach the relatively high and broadband optical absorption of Si-nc was exploited, keeping the advantages of a near-infrared inorganic light emitter. Another fundamental part of the assessment of Si-nc for bioimaging is their biocompatibility. Here, we report toxicity tests based on the lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays on epithelial cells and fibroblasts, confirming that Si-nc in concentration suitable for luminescent labeling do not affect significantly the cells viability. © Materials Research Society 2012
Study of defect-related light emission in oxidized silicon nanocrystals
No full textLuminescence from surface oxidized silicon nanocrystals (Si-nc) is an intriguing phenomenon with great potential for applications. Full consensus on the source of optical emission is not yet reached despite the huge research effort devoted to this topic. In this paper we report new evidence supporting a defect-related emission mechanism. In particular we propose a defect-based model to interpret the photoluminescence (PL) emission from partially oxidized Si-nc after thermal annealing in air. The PL emission is first studied in the time-dependent regime, using an approach based on discrete light-emitters. The results of this analysis are then exploited for elucidation of continuous wave (CW) data. Using our model the dependence of the PL emission spectrum on the excitation power and the shortening of the time decays at increasing pump power can be explained in terms of the different saturation behavior of luminescent defects. Moreover a rate equation approach for the coupled system composed by the Si-nc core and the associated luminescent defects is used to interpret the luminescence rise-time data under pulsed excitation. In this way the consistency of our picture is verified. Attribution of luminescent defects to non-bridging hole centers combined with oxygen vacancies in the oxide layer capping the Si-nc allows for a preliminary understanding of the increase of luminescence emission intensity and of the variation of its spectral features with the thermal annealing conditions
Thermal diffusivity enhancement in nanofluids based on pyrolytic titania nanopowders: Importance of aggregate morphology
No full textNanoparticle suspensions (nanofluids) have been subject of several investigations in the last few years for their potential applications, one of them being the improvement of heat transfer characteristics of thermal fluids. However, notwithstanding the numerous studies on thermal properties of nanofluids containing various kinds of nanoparticles, in many cases, the results are conflicting, and the models proposed to explain the experiments are controversial. In this paper, the thermal conductivity enhancement in dispersions, based on titania nanoparticles produced by laser-assisted pyrolysis, is investigated using an optical technique known as forced Rayleigh light scattering. Measurements on these systems exhibited a linear relation between the thermal conductivity enhancement and the nanoparticle volume fractions with a maximum increase of 6% with respect to the base fluid ethanol at 0.6% titania content. Comparison of the experimental data with the aggregation model developed by Prasher et al. highlighted the crucial role of the morphology of pyrolytic nanoparticle aggregates on determining the thermal conductivity enhancement. Copyright © 2014 John Wiley & Sons, Ltd
Perspectives of application for nanoparticles prepared by CO2 laser pyrolysis: From ceramic nanocomposites to nanofluids
No full textNanoparticles are one of the main ingredients for the realization of a wide range of nanostructured materials and devices with potential applications in several research areas and industrial sectors, hence their synthesis is a critical step in the development of nanotechnologies. Here we report on the preparation of several types of nanoparticles by laser pyrolysis of gas phase or vapour phase precursors, a very flexible and scalable synthesis route. A critical insight is given into the perspectives of practical applications of these nanoparticles in a number of fields ranging from the fabrication of ceramic nanocomposites to wear resistant coatings, from fluorophores for bio-imaging to nanofluids for efficient thermal management, from nanocoatings for cultural heritage preservation to the realization of a new class of inks for ink-jet printing applications. © Società Italiana di Fisica
Le nuove frontiere della sensoristica. Fotosensori a stato solido a base di TiO2 per il controllo dell'ambiente e degli alimenti
No full textThe effect factor for nano TiO2: preliminary toxicity tests on Daphnia magna and future developments
No full textNanotechnologies are being developed for application in a large variety of sectors, from food industry to environmental remediation technology. However, numerous uncertainties exist regarding their possible impacts on the environment and human health. The Life Cycle Assessment (LCA) methodology could be a tool to evaluate, analyze and manage the environmental and health effects for the emerging technologies. The evaluation of the environmental performance of nanotechnologies trough LCA is not always possible due to the lack of data regarding the environmental pathway of NPs. The focus of the present research is to evaluate the freshwater ecotoxicological Effect Factor (EF) for TiO2 nanoparticles (which are widely used in different applications as sunscreens, solar cells, ecc.), following the framework of the USEtox model. This model is used for the Life Cycle Impact Assessment (LCIA) phase and is aimed to provide the Characterization Factor (CF) for the ecotoxicity impact category. The CF is quantified trough the evaluation of the Fate Factor (FF) and Effect Factor (EF). The latter is based on chronic or acute toxicity value as EC50. In order to establish the acute EC50 for nano TiO2, two preliminary toxicity tests on Daphnia magna (72h) have been performed. The particles were prepared following two different treatments. In the first case the nano TiO2 suspensions were stirred for 24 h only before the test; in the second case the particles were maintained in agitation also for the whole duration of the bioassay. No adverse effects have been observed for the concentration applied, this contrasts with the findings of other studies that reported effects of nano TiO2 on D. magna. The future developments of our research are to conduct other toxicity tests on D. magna, following different treatments of the sample (example: irradiation with UV-A, filtration etc), and to conduct toxicity test on different trophic level (algae, crustaceans, fish) as suggested by USEtox framework. The research is intended to identify suitable treatments for nanoparticles to be used in toxicity test, taking into account their tendency to aggregate and precipitate and that this could influence the results of the tests. The suitable treatment should also reproduce the actual exposure modality of the organisms in the field
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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