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| 2. |
- Damgaard, P. D., et al.
(författare)
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137 ancient human genomes from across the Eurasian steppes
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 557:7705, s. 369-374
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Tidskriftsartikel (refereegranskat)abstract
- For thousands of years the Eurasian steppes have been a centre of human migrations and cultural change. Here we sequence the genomes of 137 ancient humans (about 1x average coverage), covering a period of 4,000 years, to understand the population history of the Eurasian steppes after the Bronze Age migrations. We find that the genetics of the Scythian groups that dominated the Eurasian steppes throughout the Iron Age were highly structured, with diverse origins comprising Late Bronze Age herders, European farmers and southern Siberian hunter-gatherers. Later, Scythians admixed with the eastern steppe nomads who formed the Xiongnu confederations, and moved westward in about the second or third century bc, forming the Hun traditions in the fourthfifth century ad, and carrying with them plague that was basal to the Justinian plague. These nomads were further admixed with East Asian groups during several short-term khanates in the Medieval period. These historical events transformed the Eurasian steppes from being inhabited by Indo-European speakers of largely West Eurasian ancestry to the mostly Turkic-speaking groups of the present day, who are primarily of East Asian ancestry.
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| 3. |
- Ferri, Julien, 1990, et al.
(författare)
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Enhancement of laser-driven ion acceleration in non-periodic nanostructured targets
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:1
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Tidskriftsartikel (refereegranskat)abstract
- Using particle-in-cell simulations, we demonstrate an improvement of the target-normal-sheath acceleration (TNSA) of protons in non-periodically nanostructured targets with micron-scale thickness. Compared to standard flat foils, an increase in the proton cutoff energy by up to a factor of two is observed in foils coated with nanocones or perforated with nanoholes. The latter nano-perforated foils yield the highest enhancement, which we show to be robust over a broad range of foil thicknesses and hole diameters. The improvement of TNSA performance results from more efficient hot-electron generation, caused by a more complex laser-electron interaction geometry and increased effective interaction area and duration. We show that TNSA is optimized for a nanohole distribution of relatively low areal density and that is not required to be periodic, thus relaxing the manufacturing constraints.
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| 4. |
- Grigorenko, L, et al.
(författare)
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Scientific program of DERICA-prospective accelerator and storage ring facility for radioactive ion beam research
- 2019
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Ingår i: Physics-Uspekhi. - 1468-4780 .- 1063-7869. ; 62:7, s. 675-690
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Tidskriftsartikel (refereegranskat)abstract
- Studies of radioactive ions (RIs) are the most thriving field of low-energy nuclear physics. In this paper, the concept and the scientific agenda of the prospective accelerator and storage ring facility for RI beam (RIB) research are proposed for a large-scale international project based at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research. The motivation for the new facility is discussed and its characteristics are briefly presented and shown to be comparable to those of advanced world centers, the so-called "RIB factories". In the project, the emphasis is made on studies with short-lived RIBs in storage rings. A unique feature of the project is the possibility of studying electron-RI interactions in a collider experiment to determine the fundamental properties of nuclear matter, in particular, electromagnetic form factors of exotic nuclei.
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| 5. |
- Trompoukis, C., et al.
(författare)
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Photonic nanostructures for advanced light trapping in thin crystalline silicon solar cells
- 2015
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Ingår i: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 212:1, s. 140-155
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication, integration, and simulation, both optical and optoelectrical, of two-dimensional photonic nanostructures for advanced light trapping in thin crystalline silicon (c-Si) solar cells. The photonic nanostructures are fabricated by the combination of various lithography (nanoimprint, laser interference, and hole mask colloidal) and etching (dry plasma and wet chemical) techniques. The nanopatterning possibilities thus range from periodic to random corrugations and from inverted nanopyramids to high aspect ratio profiles. Optically, the nanopatterning results in better performance than the standard pyramid texturing, showing a more robust behavior with respect to light incidence angle. Electrically, wet etching results in higher minority carrier lifetimes compared to dry etching. From the integration of the photonic nanostructures into a micron-thin c-Si solar cell certain factors limiting the efficiencies are identified. More precisely: (a) the parasitic absorption is limiting the short circuit current, (b) the conformality of thin-film coatings on the nanopatterned surface is limiting the fill factor, and (c) the material damage from dry etching is limiting the open circuit voltage. From optical simulations, the optimal pattern parameters are identified. From optoelectrical simulations, cell design considerations are discussed, suggesting to position the junction on the opposite side of the nanopattern.
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| 6. |
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| 7. |
- Chen, W. H., et al.
(författare)
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Nanophotonics-based low-temperature PECVD epitaxial crystalline silicon solar cells
- 2016
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Ingår i: Journal of Physics D: Applied Physics. - : IOP Publishing. - 1361-6463 .- 0022-3727. ; 49:12
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Tidskriftsartikel (refereegranskat)abstract
- The enhancement of light absorption via nanopatterning in crystalline silicon solar cells is becoming extremely important with the decrease of wafer thickness for the further reduction of solar cell fabrication cost. In order to study the influence of nanopatterning on crystalline silicon thin-film solar cells, we applied two lithography techniques (laser interference lithography and nanoimprint lithography) combined with two etching techniques (dry and wet) to epitaxial crystalline silicon thin films deposited via plasma-enhanced chemical vapor deposition at 175 degrees C. The influence of nanopatterning with different etching profiles on solar cell performance is studied. We found that the etching profiles (pitch, depth and diameter) have a stronger impact on the passivation quality (open circuit voltage and fill factor) than on the optical performance (short circuit current density) of the solar cells. We also show that nanopatterns obtained via wet-etching can improve solar cell performance; and in contrast, dry-etching leads to poor passivation related to the etching profile, surface damage, and/ or contamination introduced during the etching process.
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| 8. |
- Danielsson, E., et al.
(författare)
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Characterization of heterojunction diodes with hydride vapor phase epitaxy grown AlGaN on 4H-SiC
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2372-2379
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Tidskriftsartikel (refereegranskat)abstract
- AlGaN/4H-SiC heterojunction diodes with varying composition of Al have been fabricated. Five different compositions were investigated, GaN, Al0.1Ga0.9N, Al0.15Ga0.85N, Al0.3Ga0.7N, and Al0.5Ga0.5N, along with a 4H-SiC homojunction diode for comparison. The turn on voltage was around 1 V, and the ideality factor between 1 and 2 for all heterojunction diodes except for the Al0.3Ga0.7N diode. This diode had an ideality factor between 2 and 3, and also showed a much lower series resistance, indicating a change in transport mechanism across the junction. A tunnel assisted recombination model was analyzed and compared to the extracted values of the GaN diode. The model agreed well with both current-voltage and capacitance-voltage measurements for this diode. This model was not applied to the other samples, since their characteristics could not be explained by a simple mechanism.
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| 9. |
- Danielsson, E., et al.
(författare)
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Fabrication and characterization of heterojunction diodes with HVPE-Grown GaN on 4H-SiC
- 2001
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 48:3, s. 444-449
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Tidskriftsartikel (refereegranskat)abstract
- GaN/SiC heterojunctions can improve the performance considerably for BJTs and FETs. In this work, heterojunction diodes have been manufactured and characterized. The fabricated diodes have a GaN n-type cathode region on top of a JH-SIC p-type epi layer. The GaN layer was grown with HVPE directly on off-axis SiC without a buffer layer. Mesa structures were formed and a Ti metallization was used as cathode contact to GaN, and the anode contact was deposited on the backside using sputtered Al. Both current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed on the diode structures. The ideality factor of the measured diodes was 1.1 and was constant with temperature. A built in potential of 2.06 V was extracted from I-V-measurements and agrees well with the built in potential from C-V-measurements. The conduction band offset was extracted to 1.1 eV and the heterojunction was of type II. The turn on voltage for the diodes is about 1 V lower than expected and a suggested mechanism for this effect is discussed.
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| 10. |
- Jain, S., et al.
(författare)
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Broadband absorption enhancement in ultra-thin crystalline silicon solar cells by incorporating low cost aluminum nanoparticles
- 2013
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Ingår i: 39th IEEE Photovoltaic Specialists Conference. ; , s. 555-559
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Konferensbidrag (refereegranskat)abstract
- In this study nanodisks made from aluminum are incorporated in a back-reflector scheme in order to enhance the maximum achievable current in one-micron thick crystalline silicon solar cells. We perform three-dimensional numerical investigations of the backward scattering properties of aluminum nanodisks located at the back side, and optimize them for enhancing the absorption in the silicon layer. We also compare our results with previously optimized silver nanodisks and show that Al nanodisks are nearly as efficient as Ag counterpart. We show that if the absorption in the metallic back reflector (flat metal layer) can be avoided; this results in a further enhancement in absorption in the ultra-thin silicon layer. The proposed configuration results in a broadband (500nm to 1200nm) enhancement of absorption (∼ 58 %) for ultra-thin solar cells and has a great potential in thin film photovoltaic.
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