Search results for "Engineering and Technology"
showing 10 items of 16184 documents
Laser fluence, repetition rate and pulse duration effects on paint ablation
2006
Abstract The efficiency (mm3/(J pulse)) of laser ablation of paint was investigated with nanosecond pulsed Nd:YAG lasers (λ = 532 nm) as a function of the following laser beam parameters: pulse repetition rate (1–10,000 Hz), laser fluence (0.1–5 J/cm2) and pulse duration (5 ns and 100 ns). In our study, the best ablation efficiency (η ≅ 0.3 mm3/J) was obtained with the highest repetition rate (10 kHz) at the fluence F = 1.5 J/cm2. This ablation efficiency can be associated with heat accumulation at high repetition rate, which leads to the ablation threshold decrease. Despite the low thermal diffusivity and the low optical absorption of the paint (thermal confinement regime), the ablation th…
A library of monoalkenylsilsesquioxanes as potential comonomers for synthesis of hybrid materials
2018
In this paper we demonstrate a facile and efficient synthesis of monoalkenylsubstituted POSS compounds, i.e., R7(Si8O12)-alkenyl and R7(Si8O12)(OSiMe2)-alkenyl with a functional alkenyl group of chain length (from vinyl to dec-9-enyl, with or without additional –OSiMe2– spacer between the silsesquioxane core and alkenyl moiety) and with five types of inert groups (Et, iBu, iOc, Cy, Ph) at the POSS core. These compounds constitute a library of monosubstituted POSS systems, including thorough spectroscopic and thermal characteristics. These findings could be especially useful for material chemists applying the compounds as modifiers or comonomers for copolymerization reaction, e.g., with olef…
Thermal and thermo-oxidative stability and kinetics of decomposition of PHBV/sisal composites
2017
The decomposition behaviours of composites made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and sisal were assessed in terms of thermal stability and decomposition kinetics, under inert and oxidative conditions, by means of multi-rate linear non-isothermal thermogravimetric experiments. A statistical design of experiments was applied to study the influence of the addition of sisal (0-10-20-30%wt), the presence coupling agent (Yes/No) and the applied conditions of work (inert or oxidative). An improvement of the thermal and thermo-oxidative stability of PHBV with the addition of sisal was observed for all cases. An accurate methodology based on iso-conversional methods was applied…
Applications and non-idealities of submicron Al–AlOx–Nb tunnel junctions
2016
We have developed a technique to fabricate sub-micron, 0.6µm×0.6µm Al-AlOx-Nb tunnel junctions using a standard e-beam resist, angle evaporation and double oxidation of the tunneling barrier, resulting in high quality niobium, as determined by the the high measured values of the critical temperature TC ∼ 7.5 K and the gap ∆ ∼ 1.3 meV. The devices show great promise for local nanoscale thermometry in the temperature range 1 - 7.5 K. Electrical characterization of the junctions was performed at sub-Kelvin temperatures both with and without an external magnetic field, which was used to suppress superconductivity in Al and thus bring the junction into a normal-metal-insulator-superconductor (NI…
Interactive Tools for the Preservation, Dissemination and Study of Silk Heritage—An Introduction to the SILKNOW Project
2018
Silk was a major factor for progress in Europe, mostly along the Western Silk Road’s network of production and market centers. The silk trade also allowed for the exchange of ideas and innovations, having impacts at economic, technical, functional, cultural and symbolic levels. However, silk has today become a seriously endangered heritage. Although many European specialized museums are devoted to its preservation, they usually lack the size and resources to take advantage of state-of-the-art digital technologies. The aim of this paper is twofold; firstly, we introduce SILKNOW, an interdisciplinary project that has been recently funded by the H2020 Programme of the European Union in order t…
Evaluation of web reinforcements in prestressed concrete box girders through shear-transverse bending domains
2020
In concrete box girders, the amount and distribution of reinforcements in the webs have to be estimated considering the local effects due to eccentric external loads and cross-sectional distortion and not only the global effect due to the resultant forces of a longitudinal analysis: shear, torsion and bending. This work presents an analytical model that allows designers to take into account the interaction of all these effects, global and local, for the determination of the reinforcements. The model is based on the theory of stress fields and it has been compared to a 3D finite element analysis, in order to validate the interaction domains. The results show how the proposed analytical mode…
Oxidation-responsive and "clickable" poly(ethylene glycol) via copolymerization of 2-(methylthio)ethyl glycidyl ether
2016
Poly(ethylene glycol) (PEG) is a widely used biocompatible polymer. We describe a novel epoxide monomer with methyl-thioether moiety, 2-(methylthio)ethyl glycidyl ether (MTEGE), which enables the synthesis of well-defined thioether-functional poly(ethylene glycol). Random and block mPEG-b-PMTEGE copolymers (Mw/Mn = 1.05-1.17) were obtained via anionic ring opening polymerization (AROP) with molecular weights ranging from 5 600 to 12 000 g·mol-1. The statistical copolymerization of MTEGE with ethylene oxide results in a random microstructure (rEO = 0.92 ± 0.02 and rMTEG E = 1.06 ± 0.02), which was confirmed by in situ 1H NMR kinetic studies. The random copolymers are thermorespon…
Overview of Power Electronic Switches: A Summary of the Past, State-of-the-Art and Illumination of the Future.
2020
As the need for green and effective utilization of energy continues to grow, the advancements in the energy and power electronics industry are constantly driven by this need, as both industries are intertwined for obvious reasons. The developments in the power electronics industry has over the years hinged on the progress of the semiconductor device industry. The semiconductor device industry could be said to be on the edge of a turn into a new era, a paradigm shift from the conventional silicon devices to the wide band gap semiconductor technologies. While a lot of work is being done in research and manufacturing sectors, it is important to look back at the past, evaluate the current progr…
A Study on the Assessment of Introductory Computational Thinking via Scratch Programming in Primary Schools
2018
Computational thinking (CT), a transversal intellectual foundation integral to computer science, is making its way into compulsory comprehensive education worldwide. Students are expected to attain skills and knowledge in such interdisciplinary CT principles as Algorithmic thinking, Data representation, and Debugging. Problem-solving by designing and manipulating interactive media with Scratch, a graphical programming tool, is popular especially at the primary school level. However, there has been confusion regarding how introductory CT can be operationalized for educational practice. Teachers and students need research-based knowledge for setting appropriate learning goals in addition to i…
Progress in HAXPES performance combining full-field k-imaging with time-of-flight recording
2019
Journal of synchrotron radiation 26(6), 1996-2012 (2019). doi:10.1107/S1600577519012773