| 1. |
- 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.
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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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| 2. |
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| 3. |
- Lalita, J, et al.
(författare)
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Defect evolution in MeV ion-implanted silicon
- 1996
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Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS. - : ELSEVIER SCIENCE BV. - 0168-583X. ; 120:1-4, s. 27-32
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Lightly doped silicon samples of both n- and p-type, have been implanted with low doses of H, B and Si ions using energies between 1 and 6 MeV. The resulting electrically active point defects were characterized by deep level transient spectroscopy (DLTS)
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| 4. |
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| 5. |
- Pellegrino, P., et al.
(författare)
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Annealing kinetics of vacancy-related defects in low-dose MeV self-ion-implanted n-type silicon
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 64:19
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Tidskriftsartikel (refereegranskat)abstract
- Silicon samples of n-type have been implanted at room temperature with 5.6-MeV Si-28 ions to a dose of 2 x 10(8) cm(-2) and then annealed at temperatures from 100 to 380 degreesC. Both isothermal and isochronal treatments were performed and the annealing kinetics of the prominent divacancy (V-2) and vacancy-oxygen (VO) centers were studied in detail using deep-level transient spectroscopy. The decrease Of V2 centers exhibits first-order kinetics in both Czochralski-grown (CZ) and float-zone (FZ) samples, and the data provide strong evidence for a process involving migration of V-2 and subsequent annihilation at trapping centers. The migration energy extracted for V-2 is similar to1.3 eV and from the shape of the concentration versus depth profiles, an effective diffusion length less than or equal to0.1 mum is obtained. The VO center displays a more complex annealing behavior where interaction with mobile hydrogen (H) plays a key role through the formation of VOH and VOH2 centers. Another contribution is migration of VO and trapping by interstitial oxygen atoms in the silicon lattice, giving rise to vacancy-dioxygen pairs. An activation energy of similar to 1.8 eV is deduced for the migration of VO, in close resemblance with results from previous studies using electron-irradiated samples. A model for the annealing of VO, involving only three reactions, is put forward and shown to yield a close quantitative agreement with the experimental data for both CZ and FZ samples over the whole temperature range studied.
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| 6. |
- Svensson, BG, et al.
(författare)
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Generation of vacancy-type point defects in single collision cascades during swift-ion bombardment of silicon
- 1997
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Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - : AMER INST PHYSICS. - 0163-1829. ; 55:16, s. 10498-10507
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Silicon samples of n-type have been implanted with low doses (10(7)-10(10) cm(-2)) of B-11, C-12, O-16, Si-28, Ge-74,Ge-76, and Sn-120 ions using energies between 0.4 and 8.0 MeV. Because of the low doses employed, single-collision cascades prevail, and a
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| 7. |
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