170,617 research outputs found
Sviluppo di rivestimenti in metallo duro a base di carburo di niobio spruzzato termicamente
No full textI rivestimenti termospruzzati in metallo duro WC-CoCr e Cr3C2-NiCr sono ampiamente utilizzati in componenti industriali soggetti a condizioni di lavoro severe come metodo di protezione contro usura e corrosione. Tuttavia, queste composizioni presentano restrizioni che ne limitano le applicazioni: il WC-CoCr ha incompatibilità di espansione termica con substrati in acciaio e si ossida in modo catastrofico a T>400-500°C, mentre Cr3C2-NiCr offre una minor protezione dall'usura a temperatura ambiente o moderata. Nonostante l’assenza di studi su rivestimenti termospruzzati in NbC, sono stati ottenuti risultati promettenti in termini di resistenza all'usura in un ampio intervallo di temperature usando metalli duri sinterizzati a base di NbC. In questo contesto, nel presente lavoro, diverse composizioni di rivestimenti a base di NbC sono state termospruzzate col processo High-Velocity Oxygen Fuel (HVOF) su substrati di acciaio inossidabile con l'obiettivo di raggiungere un adeguato equilibrio tra le prestazioni tribologiche e di resistenza alla corrosione. La produzione di rivestimenti a base di NbC è stata organizzata in due fasi. Nella prima fase, sono stati prodotti cermet con particelle di NbC disperse in una matrice Ni-20%Cr, con frazione volumetrica del 25% e del 40%.Nella seconda fase, le particelle di NbC sono state disperse in una frazione volumetrica del 40% di una matrice contenente Fe-25wt.%Cr-15wt.%Mo. Successivamente è stato effettuato un aggiustamento alla composizione di quest’ultima matrice, riducendone il contenuto di Mo al 6% e aggiungendo l’1wt.% di B per produrre un rivestimento più omogeneo e per ridurre l'ossidazione durante la spruzzatura. In entrambe le fasi, le particelle di NbC sono state disperse nella fase legante mediante il processo di macinazione ad alta energia (High Energy Ball Milling). Sono stati impiegati diversi set di parametri di termospruzzatura e sono state determinate la microstruttura, la microdurezza Vickers, la resistenza all'abrasione, la resistenza all'usura per strisciamento a secco (fino a 600°C) e la resistenza alla corrosione dei rivestimenti ottenuti. I risultati ottenuti sono stati confrontati con quelli raccolti su rivestimenti in metallo duro di riferimento (WC-CoCr, Cr3C2-NiCr) e su altre composizioni alternative (TiC-40NiCr e TiC-25NiCr). Indipendentemente dai parametri di processo, i rivestimenti a base di NbC hanno mostrato una bassa porosità ( 400-500 °C, while Cr3C2-NiCr offers lower wear protection at low and moderate temperatures. Despite the scarce literature on thermally sprayed NbC-based coatings, promising wear resistance results have been obtained with NbC-based bulk hardmetal formulations over a wide temperature range. In this context, in the present work, different compositions of NbC-based hardmetal coatings were sprayed by the High-Velocity Oxygen Fuel (HVOF) process on stainless steel substrates aiming to achieve an adequate balance of different tribological and electrochemical performances. The production of NbC-based coatings has been developed in two stages: in the first stage, NbC particles were homogeneously dispersed in either 25 vol.% or 40 vol.% of a Ni-20wt.%Cr matrix. In the second stage, NbC particles were dispersed in 40vol.% of a matrix containing Fe-25 wt.%Cr-15 wt.%Mo. Subsequently, an adjustment to the matrix composition was carried out: the content of Mo was reduced to 6 wt.% and the element B was added (1 wt.% on the matrix) aiming to produce a more homogeneous coating and to reduce oxidation during spraying. In both stages, the homogenization of the NbC particles in the binder phase was carried out by mechanical alloying through the process by High-Energy Ball Milling (HEBM). Different sets of thermal spray parameters were employed and the microstructure, Vickers microhardness, abrasion resistance, dry sliding wear resistance (from room temperature up to 600 °C) and corrosion resistance of the coatings were studied. The results were compared to those obtained on reference coatings (WC-CoCr, Cr3C2-NiCr) and other alternative hardmetal coatings (TiC-40NiCr and TiC-25NiCr). Regardless of the process parameters, NbC-based coatings showed low porosity (< 2%) and microhardness values of around 900 HV0.3 (NbC-25NiCr) and 1000 HV0.3 (NbC-40NiCr and NbC-FeCrMo). The NbC-NiCr coatings presented dry sliding wear resistance intermediate between those of conventional WC-CoCr and Cr3C2-NiCr coatings, and comparable to that of TiC-NiCr, despite producing higher friction coefficients. NbC-FeCrMo coatings showed low resistance to sliding wear at low and moderate temperatures (≤ 300 °C), but high resistance at high temperatures, particularly at 400 °C. All the NbC-based coatings exhibited limited three-body abrasion resistance due to the occurrence of some brittle fractures together with grooving due to abrasion. The NbC-NiCr coatings, especially the one with 40vol.% matrix phase, exhibited excellent corrosion resistance: the corrosion current densities (~0.1 μA/cm2) and passive current densities (<1 μA/cm2) were lower than the corresponding values found for all reference coatings. Thus, NbC-NiCr coatings are promising for applications where a good balance between corrosion resistance and wear resistance over a wide temperature range is required, while the NbC-FeCrMo coating is particularly promising for sliding wear applications at 400°C
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Zum Verhältnis von Unternehmens- und Kulturgeschichte
No full textKleinöder N, Marx C, Gehlen B, Czierpka J, Derix S, Lutz M. Zum Verhältnis von Unternehmens- und Kulturgeschichte. In: Neue Perspektiven der Unternehmensgeschichte. Brill | Schöningh; 2024: 37-55
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
No full textWe 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
Projected pH reductions by 2100 might put deep North Atlantic biodiversity at risk
No full textThis study aims to evaluate the potential for impacts of ocean acidification on North Atlantic deep-sea ecosystems in response to IPCC AR5 Representative Concentration Pathways (RCPs). Deep-sea biota is likely highly vulnerable to changes in seawater chemistry and sensitive to moderate excursions in pH. Here we show, from seven fully coupled Earth system models, that for three out of four RCPs over 17% of the seafloor area below 500 m depth in the North Atlantic sector will experience pH reductions exceeding −0.2 units by 2100. Increased stratification in response to climate change partially alleviates the impact of ocean acidification on deep benthic environments. We report on major pH reductions over the deep North Atlantic seafloor (depth >500 m) and at important deep-sea features, such as seamounts and canyons. By 2100, and under the high CO2 scenario RCP8.5, pH reductions exceeding −0.2 (−0.3) units are projected in close to 23% (~15%) of North Atlantic deep-sea canyons and ~8% (3%) of seamounts – including seamounts proposed as sites of marine protected areas. The spatial pattern of impacts reflects the depth of the pH perturbation and does not scale linearly with atmospheric CO2 concentration. Impacts may cause negative changes of the same magnitude or exceeding the current target of 10% of preservation of marine biomes set by the convention on biological diversity, implying that ocean acidification may offset benefits from conservation/management strategies relying on the regulation of resource exploitation
Enhancing the Digital Backchannel Backstage on the Basis of a Formative User Study
No full textContemporary higher education with its large audiences suffers from passivity of students. Enhancing the classroom with a digital backchannel can contribute to establishing and fostering active participation of and collaboration among students in the lecture. Therefore, we conceived the digital backchannel Backstage specifically tailored for the use in large classes. At an early phase of development we tested its core functionalities in a small-scale user study. The aim of the study was to gain first impressions of its adoption, and also to form a basis for further steps in the conception of Backstage. Regarding adoption we particularly focused on how Backstage influences the participants' questioning behavior, a salient aspect in learning. We observed that during the study much more questions were uttered on Backstage than being asked without backchannel support. Regarding the further development of Backstage we capitalized on the participants' usability feedback. The key of the refinement is the integration of presentation slides in Backstage, which leads to an interesting reconsideration of the user interactions of Backstage
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
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
Uncovering the big players of the web
No full textIn this paper we aim at observing how today the Internet large organizations deliver web content to end users. Using one-week long data sets collected at three vantage points aggregating more than 30,000 Internet customers, we characterize the offered services precisely quantifying and comparing the performance of different players. Results show that today 65% of the web traffic is handled by the top 10 organiza- tions. We observe that, while all of them serve the same type of content, different server architectures have been adopted considering load bal- ancing schemes, servers number and location: some organizations handle thousands of servers with the closest being few milliseconds far away from the end user, while others manage few data centers. Despite this, the performance of bulk transfer rate offered to end users are typically good, but impairment can arise when content is not readily available at the server and has to be retrieved from the CDN back-en
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