| 1. |
- Lestinsky, M., et al.
(författare)
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Physics book: CRYRING@ESR
- 2016
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Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 225:5, s. 797-882
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Forskningsöversikt (refereegranskat)abstract
- The exploration of the unique properties of stored and cooled beams of highly-charged ions as provided by heavy-ion storage rings has opened novel and fascinating research opportunities in the realm of atomic and nuclear physics research. Since the late 1980s, pioneering work has been performed at the CRYRING at Stockholm (Abrahamsson et al. 1993) and at the Test Storage Ring (TSR) at Heidelberg (Baumann et al. 1988). For the heaviest ions in the highest charge-states, a real quantum jump was achieved in the early 1990s by the commissioning of the Experimental Storage Ring (ESR) at GSI Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt (Franzke 1987) where challenging experiments on the electron dynamics in the strong field regime as well as nuclear physics studies on exotic nuclei and at the borderline to atomic physics were performed. Meanwhile also at Lanzhou a heavy-ion storage ring has been taken in operation, exploiting the unique research opportunities in particular for medium-heavy ions and exotic nuclei (Xia et al. 2002).
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| 2. |
- Thorn, D. B., et al.
(författare)
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Polarization and anisotropic emission of K-shell radiation from heavy few electron ions
- 2011
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Ingår i: Canadian journal of physics (Print). - 0008-4204 .- 1208-6045. ; 89:5, s. 513-519
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Tidskriftsartikel (refereegranskat)abstract
- The population of magnetic sublevels in hydrogen-like uranium ions has been investigated in relativistic ion-atom collisions by observing the subsequent X-ray emission. Using the gas target at the experimental storage ring facility we observed the angular emission of Lyman-alpha radiation from hydrogen-like uranium ions. The alignment parameter for three different interaction energies was measured and found to agree well with theory. In addition, the use of different gas targets allowed for the electron-impact excitation process to be observed.
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| 3. |
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| 4. |
- Pustovalova, Y., et al.
(författare)
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NUScon: a community-driven platform for quantitative evaluation of nonuniform sampling in NMR
- 2021
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Ingår i: Magnetic Resonance. - : Copernicus GmbH. - 2699-0016. ; 2:2, s. 843-861
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Tidskriftsartikel (refereegranskat)abstract
- Although the concepts of nonuniform sampling (NUS) and non-Fourier spectral reconstruction in multidimensional NMR began to emerge 4 decades ago (Bodenhausen and Ernst, 1981; Barna and Laue, 1987), it is only relatively recently that NUS has become more commonplace. Advantages of NUS include the ability to tailor experiments to reduce data collection time and to improve spectral quality, whether through detection of closely spaced peaks (i.e., “resolution”) or peaks of weak intensity (i.e., “sensitivity”). Wider adoption of these methods is the result of improvements in computational performance, a growing abundance and flexibility of software, support from NMR spectrometer vendors, and the increased data sampling demands imposed by higher magnetic fields. However, the identification of best practices still remains a significant and unmet challenge. Unlike the discrete Fourier transform, non-Fourier methods used to reconstruct spectra from NUS data are nonlinear, depend on the complexity and nature of the signals, and lack quantitative or formal theory describing their performance. Seemingly subtle algorithmic differences may lead to significant variabilities in spectral qualities and artifacts. A community-based critical assessment of NUS challenge problems has been initiated, called the “Nonuniform Sampling Contest” (NUScon), with the objective of determining best practices for processing and analyzing NUS experiments. We address this objective by constructing challenges from NMR experiments that we inject with synthetic signals, and we process these challenges using workflows submitted by the community. In the initial rounds of NUScon our aim is to establish objective criteria for evaluating the quality of spectral reconstructions. We present here a software package for performing the quantitative analyses, and we present the results from the first two rounds of NUScon. We discuss the challenges that remain and present a roadmap for continued community-driven development with the ultimate aim of providing best practices in this rapidly evolving field. The NUScon software package and all data from evaluating the challenge problems are hosted on the NMRbox platform.
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| 5. |
- Cobianchi, M., et al.
(författare)
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Effects of oceanic circulation and volcanic ash-fall on calcite dissolution in bathyal sediments from the SW Pacific Ocean over the last 550 ka
- 2015
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182 .- 1872-616X. ; 429, s. 72-82
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Tidskriftsartikel (refereegranskat)abstract
- The effects on calcite dissolution of both oceanic circulation and volcanic ash-fall were evaluated in lower bathyal sediments over the last 550 ka record from core MD 97-2114, recovered on the northern slope (depth of 1936 m, in the Pacific Deep Water, PDW) of the Chatham Rise (east of New Zealand, SW Pacific Ocean). This area has been impacted by changes in glacial/interglacial circulation and ocean chemistry as well as by the explosive volcanic activity of the Taupo Volcanic Zone. Several micro-paleontological dissolution proxies, based on planktonic foraminifera and calcareous nannofossils, were analysed in order to evaluate the calcite dissolution of the deep-sea sediments. These were compared with a couple of proxies of primary productivity (benthic foraminiferal epifaunal/infaunal ratio and delta C-13(benthic) (foraminifera)) and the abundance of volcanic glass. The dissolution proxy data from MD 97-2114 were compared with two nearby ODP sites, ODP 1123 (3290 m deep, bathed by the lower Circumpolar Deep Water, LCDW) and ODP 1125 (1365 m deep, bathed by the Antarctic Intermediate Water, AAIW). The results suggest: (1) the calcite dissolution/preservation cycles at all three core sites show Glacial-Interglacial (G-I) periodicities that match the previously described "Pacific-style" CaCO3 cycles; (2) several short-term dissolution events do not follow this general scheme and occur following tephra deposition. The dissolution related to the tephra deposition seems to have mostly affected calcareous nannofossils, thus we hypothesise that the ash-fall induced a temporary reduction of the surface water pH (below 7.8), which affected the coccolithophores that inhabit the surface waters. (3) Other short-term dissolution events (1000 years) are unrelated to tephra deposition and are possibly driven by the slowing of deep-sea circulation and a reduced Deep Western Boundary Current (DWBC). This lead to the dominance of older, more corrosive Pacific Deep Water (POW) flowing in to the region, resulting in coeval dissolution episodes at all three core sites (depth range from 1365 to 3290 m).
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| 6. |
- Jiang, Qiang, et al.
(författare)
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Origin of geochemically heterogeneous mid-ocean ridge basalts from the Macquarie Ridge Complex, SW Pacific
- 2021
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Ingår i: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; 380-381
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Tidskriftsartikel (refereegranskat)abstract
- The Macquarie Ridge Complex (MRC), located at the Australian–Pacific plate boundary south of New Zealand, is a rugged bathymetric ridge comprising a series of submarine seamounts and Macquarie Island, the only subaerial portion of the complex. Mid-ocean ridge basalts (MORBs) from Macquarie Island show various enrichments in incompatible elements with compositions ranging from typical normal MORB to enriched MORB. However, these basalts have isotopic compositions trending towards a high μ-like (μ = 238U/204Pb; HIMU) mantle component, which is unusual for MORB-type rocks. The origin of this mantle signature is not understood, and it is unclear whether this isotopic signature is characteristic of the entire MRC or unique to Macquarie Island. Here we report new major and trace element abundances, and Sr, Nd, and Pb isotopes for samples from the MRC seamounts and from new sampling sites on Macquarie Island. The geochemical and isotopic data show that the entire MRC comprises normal to enriched MORB. Mixing modelling indicates that the heterogeneous isotopic signatures of the MRC basalts are not derived from contamination of the nearby Balleny mantle plume but have affinities with that of the Cenozoic Zealandia intraplate HIMU-like basalts. We propose that the heterogeneous geochemical signatures of the MRC basalts are derived from amphibole-bearing garnet pyroxenite veins, which is supported by the rare earth element partial melting modelling and strong correlations between Nd and Pb isotopic ratios vs La/Sm. We posit that the pyroxenite veins were generated in the oceanic lithospheric mantle, which was metasomatised by hydrous and carbonatitic fluids/melts derived either from delaminated, metasomatised Zealandia subcontinental lithosphere mantle, or from subducted material in the asthenosphere. The subducted material could be derived from ancient and/or recent subduction along the former east Gondwana margin.
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| 7. |
- Jiang, Qiang, et al.
(författare)
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Timing of Seafloor Spreading Cessation at the Macquarie Ridge Complex (SW Pacific) and Implications for Upper Mantle Heterogeneity
- 2021
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Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 22:1
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Tidskriftsartikel (refereegranskat)abstract
- The Macquarie Ridge Complex (MRC) on the Australia‐Pacific plate boundary south of New Zealand is an extinct mid‐ocean ridge that has experienced a complex tectonic history and produced highly heterogeneous mid‐ocean ridge basalts (MORBs). When and how seafloor spreading ceased along the proto‐Macquarie mid‐ocean ridge remain elusive, and it is unclear how the mantle source of MORBs is affected by the gradual cessation of seafloor spreading at mid‐ocean ridges. To constrain the tectonic evolution of the MRC, the mantle source variations for MORBs at dying mid‐ocean ridges, and the mechanisms of mantle enrichment and asthenospheric heterogeneities, we report 11 pyroxene, plagioclase, basaltic glass, groundmass, and sericite 40Ar/39Ar and one zircon U‐Pb ages for the MRC MORBs. Our data reveal that basalts from the MRC seamounts were erupted between 25.9 and 1.6 Ma and Macquarie Island at ∼10 Ma. Combined age and plate reconstruction results reveal that the cessation of seafloor spreading at the MRC generally propagated from south to north along the ridge. Basalts produced by the then dying Macquarie mid‐ocean ridge at different times on different seamounts/island show a large variation in isotopic compositions and there is no clear correlation between ages and isotopic ratios. The heterogeneity of mantle source for MORBs from the proto‐Macquarie mid‐ocean ridge suggests that the upper asthenospheric mantle is heterogeneous, and such heterogeneity becomes most obvious at dying mid‐ocean ridges where the degrees of partial melting are low and a large range of melt compositions are produced.
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