169,823 research outputs found
Microstructural characterisation by X-ray scattering of perovskite-type La0.8Sr0.2MnO3±d thin films prepared by a dip-coating process
Get PDFThe La0.8Sr0.2MnO3 (LSM) cathode materials are widely used in solid oxide fuel cells (SOFCs) as electronic conductors. In such materials, the reduction of oxygen is located at the triple contact boundaries: air/cathode LSM/electrolyte which is generally Yttria Stabilised Zirconia (YSZ). In order to improve the chemical reactions at these air/cathode LSM/electrolyte interfaces, the triple phase boundary length has to be optimised. In this aim, we have first synthesised the La0.8Sr0.2MnO3 phase by a sol–gel route and, second, LSM thin films have been deposited on various polished substrates by using a dip-coating process. The structure and microstructure of the resulting LSM thin layers have been investigated by using well suited complementary techniques such as X-ray reflectometry, grazing incidence small angle X-ray scattering, Xray diffraction and scanning electronic microscopy. The structural and microstructural parameters of LSM thin films have been managed and studied as a function of synthesis parameters such as initial metallic salt concentration, time and temperature of annealing. The higher the metallic salt concentration, the higher the thickness of the film, the smaller the film density.The as-prepared layers are amorphous and the single crystallised perovskite form is obtained for low temperature heat treatments. Therefore, the annealed coatings are constituted by randomly oriented LSM nanocrystals, which organise in a more or less dense close-packed microstructure according to the initial metallic salt concentration
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Evaluation of a sol–gel process for the synthesis of La1−xSrxMnO3+δ cathodic multilayers for solid oxide fuel cells
Get PDFSolid oxide fuel cells (SOFCs) are electrical energy conversion devices with high efficiency and low pollution. In order to increase performances of SOFCs at intermediate temperature (700–800 °C) and to decrease materials cost, an alternative sol–gel synthesis method has been investigated to deposit La1−xSrxMnO3+δ (LSMx) as cathode thin films. Polycrystalline LSMx thin films were prepared by dip-coating using a polymeric solution. Lanthanum, strontium and manganese nitrates were used as raw materials. The viscosity of the solution was adjusted and the solution was deposited on polycrystalline ZrO2–8% Y2O3 ceramics. Prior to experiments, the substrate surface was eroded until a roughness of 20 nm and then cleaned with ethanol and dried. Film thicknesses were adjusted with the number of layers. Porosity and grain size of monolayers or multilayers were evaluated. Typical thickness of monolayer is 250 nm. A key parameter in the multilayer process was the intermediate calcination temperature (400, 700 or 1000 °C) of each further layer deposition. A correlation between this intermediate temperature and morphology, thickness and porosity was found; porosity is ranging from 3 to 40% and thickness can reach 1 micron for multilayers. Concerning electrochemical performances, the best results were obtained for LSM0.4 multilayers with an intermediate calcination temperature (called Ti) of 400 °C
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Optimization of Micro-SOFC Performance through the Control of the Architecture Using a Low Cost Process
No full textInternational audienceMicro-SOFCs (μSOFCs) have been attracting much attention because of reducing operating temperature, their potential as long lasting, rapid re-charging, lightweight portable power sources. They have been demonstrated to exhibit good power density at temperatures as low as 600°C. To be cost competitive and relevant for widespread use, it is crucial to explore the synthesis of thin film via soft-chemistry less expensive than physical ones (PLD, ALD...). Combining dip-coating and sol-gel processes, nanometer scale 10%gadolinium doped ceria (GDC, electrolyte), LSCF (cathode) and 10%GDC-nickel based composite nanoarchitectures films were deposited on a Si wafer and on porous Al2O3 substrates in one-step thermal processing. For the electrodes, the 3-D network is constituted of non-agglomerates nanoparticles of Gd-doped ceria and NiO or LSCF. In this arrangement, particles in the nanoscale are kept because of the presence of secondary phases (NiO, LSCF) and pores. The different interfaces in these hierarchical-porous composites tune the particles size as well as the surface energy. The study of the microstrain through XRD analyses shows that the domain of stability of the studied microstructure is large (200°C) for NiO/GDC cermet. Accordingly, the effect of the microstructure on the mixed ionic conductivities in this range of temperature is low, because their microstructure is stable. These composites can be used as model for understanding the impact of the size of the particle on the transport of ions and electrons. Furthermore, the reduction of the NiO/GDC electrodes were studied through various techniques: XRD, ac-impedance. The microstructures were stable up to temperatures of 600°C. The electrochemical performances I-V curves of these different thin layers were measured in a single gas atmosphere setup. The electrochemical results will be discussed as function of the cathode and anode composition and the microstructure (the temperature and the reducing treatments). Finally, these different hierarchical-porous thin films are favorable for efficient composite electrode and electrolyte for micro-SOFC application. 1. A. Evans et al., Journal of Power Sources, 2009, 194, 119-129. 2. J. Hierso, O. Sel, A. Ringuede, C. Laberty-Robert, L Bianchi, D. Grosso, and C. Sanchez, Chem. Mater. 2009, 21, 2184-2192 3. G. Muller, G. Baldinozzi, C. Laberty-Robert, C. Sanchez, 2011, submite
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
Optimization of Micro-SOFC Performance through the Control of the Architecture Using a Low Cost Process
No full textInternational audienceMicro-SOFCs (μSOFCs) have been attracting much attention because of reducing operating temperature, their potential as long lasting, rapid re-charging, lightweight portable power sources. They have been demonstrated to exhibit good power density at temperatures as low as 600°C. To be cost competitive and relevant for widespread use, it is crucial to explore the synthesis of thin film via soft-chemistry less expensive than physical ones (PLD, ALD...). Combining dip-coating and sol-gel processes, nanometer scale 10%gadolinium doped ceria (GDC, electrolyte), LSCF (cathode) and 10%GDC-nickel based composite nanoarchitectures films were deposited on a Si wafer and on porous Al2O3 substrates in one-step thermal processing. For the electrodes, the 3-D network is constituted of non-agglomerates nanoparticles of Gd-doped ceria and NiO or LSCF. In this arrangement, particles in the nanoscale are kept because of the presence of secondary phases (NiO, LSCF) and pores. The different interfaces in these hierarchical-porous composites tune the particles size as well as the surface energy. The study of the microstrain through XRD analyses shows that the domain of stability of the studied microstructure is large (200°C) for NiO/GDC cermet. Accordingly, the effect of the microstructure on the mixed ionic conductivities in this range of temperature is low, because their microstructure is stable. These composites can be used as model for understanding the impact of the size of the particle on the transport of ions and electrons. Furthermore, the reduction of the NiO/GDC electrodes were studied through various techniques: XRD, ac-impedance. The microstructures were stable up to temperatures of 600°C. The electrochemical performances I-V curves of these different thin layers were measured in a single gas atmosphere setup. The electrochemical results will be discussed as function of the cathode and anode composition and the microstructure (the temperature and the reducing treatments). Finally, these different hierarchical-porous thin films are favorable for efficient composite electrode and electrolyte for micro-SOFC application. 1. A. Evans et al., Journal of Power Sources, 2009, 194, 119-129. 2. J. Hierso, O. Sel, A. Ringuede, C. Laberty-Robert, L Bianchi, D. Grosso, and C. Sanchez, Chem. Mater. 2009, 21, 2184-2192 3. G. Muller, G. Baldinozzi, C. Laberty-Robert, C. Sanchez, 2011, submite
A 0.12mm<sup>2</sup> Wien-Bridge Temperature Sensor with 0.1°C (3σ) Inaccuracy from -40°C to 180°C
No full text Resistor-based temperature sensors can achieve much higher resolution and energy efficiency than conventional BJT-based sensors [1], but they typically occupy more area (> 0.25 mm 2 ) and have lower operating temperatures (le 125 {circ} {C}) [2]-[4]. This work describes a 0.12mm 2 resistor-based sensor that uses a Wien-bridge (WB) filter to achieve 0.1 {circ} {C} (3 sigma) inaccuracy from - 40 {circ} {C} to 180 {circ} {C}. Compared to a state-of-the-art WB sensor [4], it occupies 6 × less area and achieves comparable relative accuracy over a 76% wider operating range. Session 10.3 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
A ±25A Versatile Shunt-Based Current Sensor with 10kHz Bandwidth and ±0.25% Gain Error from -40°C to 85°C Using 2-Current Calibration
No full textAccurate current sensing is critical in many industrial applications, such as battery management and motor control. Precise shunt-based current sensors have been reported with gain errors of less than 1% over the industrial temperature range (-40°C to 85°C) [1]–[4]. However, since they are intended for coulomb counting, their bandwidth is limited to a few tens of Hz, making them unsuitable for battery impedance or motor-current sensing. This paper presents a current sensor with a wide (10kHz) bandwidth and a tunable temperature compensation scheme (TCS), which allows it to be flexibly used with different types of shunts while maintaining high accuracy. A low-cost room-temperature calibration scheme is proposed to optimize gain flatness over temperature by exploiting the shunt's self-heating at large currents. Over the industrial temperature range and a ±25A current range, it achieves state-of-the-art gain error (±0.25%) with both low-cost PCB and stable metal-alloy shunts.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
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