| 1. |
- De Marco, O., et al.
(författare)
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The messy death of a multiple star system and the resulting planetary nebula as observed by JWST
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:12, s. 1421-1432
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Tidskriftsartikel (refereegranskat)abstract
- Planetary nebulae—the ejected envelopes of red giant stars—provide us with a history of the last, mass-losing phases of 90% of stars initially more massive than the Sun. Here we analyse images of the planetary nebula NGC 3132 from the James Webb Space Telescope (JWST) Early Release Observations. A structured, extended hydrogen halo surrounding an ionized central bubble is imprinted with spiral structures, probably shaped by a low-mass companion orbiting the central star at about 40–60 au. The images also reveal a mid-infrared excess at the central star, interpreted as a dusty disk, which is indicative of an interaction with another closer companion. Including the previously known A-type visual companion, the progenitor of the NGC 3132 planetary nebula must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionization and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Furthermore, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star with excellent precision: 2.86 ± 0.06 M⊙. These results serve as pathfinders for future JWST observations of planetary nebulae, providing unique insight into fundamental astrophysical processes including colliding winds and binary star interactions, with implications for supernovae and gravitational-wave systems.
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| 2. |
- Kaschuk, J. J., et al.
(författare)
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Processing factors affecting roughness, optical and mechanical properties of nanocellulose films for optoelectronics
- 2024
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Ingår i: Carbohydrate Polymers. - : Elsevier Ltd. - 0144-8617 .- 1879-1344. ; 332
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Tidskriftsartikel (refereegranskat)abstract
- This work aims to understand how nanocellulose (NC) processing can modify the key characteristics of NC films to align with the main requirements for high-performance optoelectronics. The performance of these devices relies heavily on the light transmittance of the substrate, which serves as a mechanical support and optimizes light interactions with the photoactive component. Critical variables that determine the optical and mechanical properties of the films include the morphology of cellulose nanofibrils (CNF), as well as the concentration and turbidity of the respective aqueous suspensions. This study demonstrates that achieving high transparency was possible by reducing the grammage and adjusting the drying temperature through hot pressing. Furthermore, the use of modified CNF, specifically carboxylated CNF, resulted in more transparent films due to a higher nanosized fraction and lower turbidity. The mechanical properties of the films depended on their structure, homogeneity (spatial uniformity of local grammage), and electrokinetic factors, such as the presence of electrostatic charges on CNF. Additionally, we investigated the angle-dependent transmittance of the CNF films, since solar devices usually operate under indirect light. This work demonstrates the importance of a systematic approach to the optimization of cellulose films, providing valuable insight into the optoelectronic field.
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| 3. |
- Li, Tian, et al.
(författare)
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Developing fibrillated cellulose as a sustainable technological material
- 2021
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Ingår i: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 590:7844, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose is the most abundant biopolymer on Earth, found in trees, waste from agricultural crops and other biomass. The fibres that comprise cellulose can be broken down into building blocks, known as fibrillated cellulose, of varying, controllable dimensions that extend to the nanoscale. Fibrillated cellulose is harvested from renewable resources, so its sustainability potential combined with its other functional properties (mechanical, optical, thermal and fluidic, for example) gives this nanomaterial unique technological appeal. Here we explore the use of fibrillated cellulose in the fabrication of materials ranging from composites and macrofibres, to thin films, porous membranes and gels. We discuss research directions for the practical exploitation of these structures and the remaining challenges to overcome before fibrillated cellulose materials can reach their full potential. Finally, we highlight some key issues towards successful manufacturing scale-up of this family of materials. Opportunities for the application of fibrillated cellulose materials-which can be extracted from renewable resources-and broader manufacturing issues of scale-up, sustainability and synergy with the paper-making industry are discussed.
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| 4. |
- Sanhueza, J. P., et al.
(författare)
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Computational modeling of the effect of B and W in the phase transformation of M23C6 carbides in 9 to 12 pct Cr martensitic/ferritic steels
- 2019
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Ingår i: Materials Research Express. - : IOP PUBLISHING LTD. - 2053-1591. ; 6:11
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Tidskriftsartikel (refereegranskat)abstract
- The effect of B and W in the precipitation kinetic of M23C6 carbides in martensitic/ferritic steels were studied assisted by ThermoCalc and TC-PRISMA. The simulation predicts that B has low solubility in the austenitic and ferritic matrix, thus promoting the formation of M2B borides and (Cr, Fe)(23)(C, B)(6) carbides. Furthermore, calculation carried out in ThermoCalc shown that M2B borides are stable even at austenization temperature (1100 degrees C). This suggests that in martensitic/ferritic steels M2B precipitates first, hence consuming most of available B. Additionally, the precipitation kinetics of (Cr, Fe)(23)C-6, (Cr, Fe, W)(23)C-6 and (Cr, Fe)(23)(C, B)(6) were simulated in TC-PRISMA, results obtained predict a higher steady nucleation rate for the latter. When B atoms incorporate to (Cr, Fe)(23)C-6 reduces the interfacial energy from 0.26 J/m(2) to 0.17 J m(-2), which indicates a smaller misfit between (Cr, Fe)(23)(C, B)(6) carbides and matrix. On the other hand, B and W reduce the coarsening rate of M23C6 carbides by decreasing the interfacial energy and reducing diffusivities, respectively. Theoretical results compared with experimental data of the coarsening rate of (Cr, Fe, W)(23)(C, B)(6) shown that it is one order of magnitude lower than the predicted by TC-PRISMA. This suggests that B can be the rate-controlling element of the coarsening of (Cr, Fe, W)(23)(C, B)(6) carbides instead of W.
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| 5. |
- Sanhueza, J. P., et al.
(författare)
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Effect of Boron in the Coarsening Rate of Chromium-Rich Carbides in 9%–12% Chromium Martensitic Creep-Resistant Steel : Experiment and Modeling at 650 °C
- 2020
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Ingår i: Metals and Materials International. - : Korean Institute of Metals and Materials. - 1598-9623 .- 2005-4149.
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: In this study, three martensitic creep-resistant steels with 100, 90, and 70 ppm of boron were investigated. The experimental data obtained from isothermal aging and creep test at 650 °C were compared with the results of simulation conducted using TC-PRISMA software. Tungsten was found to be the rate-controlling element in the coarsening of (Cr, Fe, W)23C6 carbides; however, this result differed in terms of boron-containing steel. Several studies indicate that the low solubility of boron in ferrite promotes boron enrichment in (Cr, Fe, W)23C6 carbide, thereby reducing its coarsening rate. However, this mechanism is not universally agreed upon. In the present study, a comparison between experimental and theoretical results revealed that in boron-containing steels, the coarsening of (Cr, Fe, W)23C6 carbide is controlled probably by boron volume diffusion or by trans-interface diffusion. Graphic Abstract: [Figure not available: see fulltext.].
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| 6. |
- Bombois, Xavier, et al.
(författare)
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Optimal experiment design for hypothesis testing applied to functional magnetic resonance imaging
- 2011
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Ingår i: Proceedings of the 18th IFAC World Congress. ; , s. 9953-9958
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Konferensbidrag (refereegranskat)abstract
- Hypothesis testing is a classical methodology of making decisions using experimental data. In hypothesis testing one seeks to discover evidence that either accepts or rejects a given null hypothesis H0. The alternative hypothesis H1 is the hypothesis that is accepted when H0 is rejected. In hypothesis testing, the probability of deciding H1 when in fact H0 is true is known as the false alarm rate, whereas the probability of deciding H1when in fact H1is true is known as the detection rate (or power) of the test. It is not possible to optimize both rates simultaneously. In this paper, we consider the problem of determining the data to be used for hypothesis testing that maximize the detection rate for a given false alarm rate. We consider in particular a hypothesis test which is relevant in functional magnetic resonance imaging (fMRI).
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| 7. |
- Oñate, A., et al.
(författare)
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Production of Nb-doped super duplex stainless steel based on recycled material : A study of the microstructural characterization, corrosion, and mechanical behavior
- 2023
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Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584 .- 1879-3312. ; 308
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Tidskriftsartikel (refereegranskat)abstract
- The corrosion behavior of a new Nb-doped stainless steel (SDSS-Nb) designed by the CALPHAD method, produced using an open atmosphere process based on recycled materials, was investigated to improve the circular economy. Three heat-treatment conditions were evaluated to assess the sensitization effects of the precipitates and inclusions. XRD and SEM-EDS were used for phase identification, and sensitization was analyzed by cyclic polarization and Scanning Kelvin Probe Force Microscopy (SKPFM). The thermodynamic stability predicted by Thermo-Calc agrees with that observed by SEM-EDS. It was observed by cyclic polarization that the corrosion sensitization was mainly provided by the σ phase, which was deduced from the results obtained by SEM-EDS, XRD, and Thermo-Calc simulations. Furthermore, it was obtained that the sensitization due to Cr2N precipitates and nonmetallic inclusions was low, and the mechanical response is comparable to commercial UNS32750 super duplex stainless steel, which allows a good performance in severe environments and an efficient industrial application. Additionally, it has been obtained by SKPFM that the shear potential between the σ phase and the austenite is between 210 mV and 241 mV and that its value depends on the stability and equilibrium reached by the σ phase during thermal cycling.
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| 8. |
- Santana, Felipe A., et al.
(författare)
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Final Targeting Strategy for the SDSS-IV APOGEE-2S Survey
- 2021
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 162:6
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Tidskriftsartikel (refereegranskat)abstract
- APOGEE is a high-resolution (R similar to 22,000), near-infrared, multi-epoch, spectroscopic survey of the Milky Way. The second generation of the APOGEE project, APOGEE-2, includes an expansion of the survey to the Southern Hemisphere called APOGEE-2S. This expansion enabled APOGEE to perform a fully panoramic mapping of all of the main regions of the Milky Way; in particular, by operating in the H band, APOGEE is uniquely able to probe the dust-hidden inner regions of the Milky Way that are best accessed from the Southern Hemisphere. In this paper we present the targeting strategy of APOGEE-2S, with special attention to documenting modifications to the original, previously published plan. The motivation for these changes is explained as well as an assessment of their effectiveness in achieving their intended scientific objective. In anticipation of this being the last paper detailing APOGEE targeting, we present an accounting of all such information complete through the end of the APOGEE-2S project; this includes several main survey programs dedicated to exploration of major stellar populations and regions of the Milky Way, as well as a full list of programs contributing to the APOGEE database through allocations of observing time by the Chilean National Time Allocation Committee and the Carnegie Institution for Science. This work was presented along with a companion article, Beaton et al. (2021), presenting the final target selection strategy adopted for APOGEE-2 in the Northern Hemisphere.
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| 9. |
- Feng, Zhaoxuan
(författare)
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From Polysaccharides to Functional Materials for Trace Pharmaceutical Adsorption
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transition to bioeconomy will reduce our dependency on fossil fuels as well as contribute to a more sustainable society. Within this framework, exploitation and development of renewable substitutes to petroleum-based products provides feasible roadmap for the material design. Here a perspective is provided to how the natural polysaccharides chitosan (CS) and/or cellulose (CL) could be elaborated and transformed to high-performance materials with the explicit aim of removing trace pharmaceutical contaminants from the wastewater, thus facilitating the sustainable development. In the first part of the thesis, chitosan and cellulose were converted to the carbon spheres (C-sphere) through a microwave-assisted hydrothermal carbonization process, and C-sphere was further broken down to the nanographene oxide (nGO) via a simple oxidation route. On this foundation, a green pathway was developed for fabrication of biobased materials for wastewater purification. First, macroporous chitosan-based composite hydrogels with controllable properties were developed, where chitosan-derived nGO worked as a functional property enhancer. Second, a further development changing from the bulky hydrogels to microgels consisting of CS composite particles in the microscopic size was achieved by a fast one-pot spraying-drying process. The crosslinking reaction occurred in situ during the spray-drying. Last, the C-sphere by-itself was also believed to be a potential adsorbent for wastewater contaminants. In the next step the prepared systems were evaluated for their capacity to adsorb pharmaceutical contaminants. Diclofenac sodium (DCF) was utilized as the model drug, and the three fabricated bio-adsorbents all demonstrated effective DCF adsorption performance, with the adsorption efficiency varying from 65.6 to 100%. Moreover, the DCF adsorption kinetics, isotherms and thermodynamic study were also investigated to reveal the nature of the adsorption process with the different materials. Finally, chitosan-based microspheres were selected for the reusability study, with the adsorption efficiency above 70% retained after six adsorption-desorption cycles, thus further endowing the promising potential of the fabricated bio-adsorbents for commercial applications.
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| 10. |
- Abidnejad, Roozbeh, et al.
(författare)
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Gas evolution in self-extinguishing and insulative nanopolysaccharide-based hybrid foams
- 2024
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Ingår i: Carbohydrate Polymers. - : Elsevier Ltd. - 0144-8617 .- 1879-1344. ; 346
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Tidskriftsartikel (refereegranskat)abstract
- Lightweight, energy-efficient materials in building construction typically include polymeric and composite foams. However, these materials pose significant fire hazards due to their high combustibility and toxic gas emissions, including carbon monoxide and hydrogen cyanide. This study delves into the latter aspects by comparing hybrid systems based on nanofiber-reinforced silica-based Pickering foams with a synthetic reference (polyurethane foams). The extent and dynamics of fire retardancy and toxic gas evolution were assessed, and the results revealed the benefits of combining the thermal insulation of silica with the structural strength of biobased nanofibers, the latter of which included anionic and phosphorylated cellulose as well as chitin nanofibers. We demonstrate that the nanofiber-reinforced silica-based Pickering foams are thermal insulative and provide both fire safety and energy efficiency. The results set the basis for the practical design of hybrid foams to advance environmental sustainability goals by reducing energy consumption in built environments.
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