| 1. |
- Gómez-Barea, Alberto, et al.
(författare)
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Improving the performance of fluidized bed biomass/waste gasifiers for distributed electricity: A new three-stage gasification system
- 2013
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 50:2, s. 1453-1462
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Tidskriftsartikel (refereegranskat)abstract
- Methods to increase the conversion of char and tar in fluidized bed gasifiers (FBG) are discussed, with thefocus on small to medium-size biomass/waste gasifiers for power production (from 0.5 to 10 MWe).Optimization of such systems aims at (i) maximizing energy utilization of the fuel (maximizing charconversion), (ii) minimizing secondary treatment of the gas (by avoiding complex tar cleaning), and(iii) application in small biomass-to-electricity gasification plants. The efficiency of various measures toincrease tar and char conversion within a gasification reactor (primary methods) is discussed. The optimizationof FBG by using in-bed catalysts, by addition of steam and enriched air as gasification agent, andby secondary-air injection, although improving the process, is shown to be insufficient to attain the gaspurity required for burning the gas in an engine to produce electricity. Staged gasification is identified asthe only method capable of reaching the targets mentioned above with reasonable simplicity and cost, so itis ideal for power production. A promising new stage gasification process is presented. It is based on threestages: FB devolatilization, non-catalytic air/steam reforming of the gas coming from the devolatilizer, andchemical filtering of the gas and gasification of the char in a moving bed supplied with the char generatedin the devolatilizer. Design considerations and comparison with one-stage FBG are discussed.
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| 2. |
- Hernández, Ángela Saá, et al.
(författare)
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A new imaging technology based on Compton X-ray scattering
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 1558-1572
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Tidskriftsartikel (refereegranskat)abstract
- A feasible implementation of a novel X-ray detector for highly energetic X-ray photons with a large solid angle coverage, optimal for the detection of Compton X-ray scattered photons, is described. The device consists of a 20 cm-thick sensitive volume filled with xenon at atmospheric pressure. When the Compton-scattered photons interact with the xenon, the released photoelectrons create clouds of secondary ionization, which are imaged using the electroluminescence produced in a custom-made multi-hole acrylic structure. Photon-by-photon counting can be achieved by processing the resulting image, taken in a continuous readout mode. Based on Geant4 simulations, by considering a realistic detector design and response, it is shown that photon rates up to at least 1011photons s-1on-sample (5 μm water-equivalent cell) can be processed, limited by the spatial diffusion of the photoelectrons in the gas. Illustratively, if making use of the Rose criterion and assuming the dose partitioning theorem, it is shown how such a detector would allow obtaining 3D images of 5 μm-size unstained cells in their native environment in about 24 h, with a resolution of 36 nm.
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| 3. |
- Jones, Geraint H., et al.
(författare)
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The Comet Interceptor Mission
- 2024
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Ingår i: Space Science Reviews. - : Springer Nature. - 0038-6308 .- 1572-9672. ; 220:1
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Tidskriftsartikel (refereegranskat)abstract
- Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum Δ V capability of 600 ms − 1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.
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| 4. |
- Perez-Escobar, Oscar A., et al.
(författare)
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The origin and speciation of orchids
- 2024
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Ingår i: NEW PHYTOLOGIST. - 0028-646X .- 1469-8137. ; 242:2, s. 700-716
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Tidskriftsartikel (refereegranskat)abstract
- Orchids constitute one of the most spectacular radiations of flowering plants. However, their origin, spread across the globe, and hotspots of speciation remain uncertain due to the lack of an up-to-date phylogeographic analysis. We present a new Orchidaceae phylogeny based on combined high-throughput and Sanger sequencing data, covering all five subfamilies, 17/22 tribes, 40/49 subtribes, 285/736 genera, and c. 7% (1921) of the 29 524 accepted species, and use it to infer geographic range evolution, diversity, and speciation patterns by adding curated geographical distributions from the World Checklist of Vascular Plants. The orchids' most recent common ancestor is inferred to have lived in Late Cretaceous Laurasia. The modern range of Apostasioideae, which comprises two genera with 16 species from India to northern Australia, is interpreted as relictual, similar to that of numerous other groups that went extinct at higher latitudes following the global climate cooling during the Oligocene. Despite their ancient origin, modern orchid species diversity mainly originated over the last 5 Ma, with the highest speciation rates in Panama and Costa Rica. These results alter our understanding of the geographic origin of orchids, previously proposed as Australian, and pinpoint Central America as a region of recent, explosive speciation.
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| 5. |
- Villanueva, Diego, et al.
(författare)
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Constraining the Impact of Dust-Driven Droplet Freezing on Climate Using Cloud-Top-Phase Observations
- 2021
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Ingår i: Geophysical Research Letters. - 1944-8007 .- 0094-8276. ; 48:11
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Tidskriftsartikel (refereegranskat)abstract
- Despite advances in our understanding of ice-nucleating particles, the effect of cloud glaciation on the Earth's radiation balance has remained poorly constrained. Particularly, dust ice nuclei are believed to enhance cloud glaciation in the Northern Hemisphere. We used satellite observations of the hemispheric and seasonal contrast in cloud top phase to assess the dust-driven droplet freezing in a climate model. The required freezing efficiency for dust ice nuclei suggests that climate models glaciate too few clouds through immersion droplet freezing. After tuning, the model leads to more realistic cloud-top-phase contrasts and a dust-driven glaciation effect of 0.14 ± 0.13 W m−2 between 30°N and 60°N. Observations of cloud-top-phase contrasts provide a strong constraint for ice formation in mixed-phase clouds and may provide a weak constraint for the associated impact on radiation and precipitation. Future studies should therefore consider both the mean-state cloud-phase partitioning and cloud-phase contrasts to achieve a more accurate simulation of dust-driven cloud glaciation.
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