| 1. |
- Heuer, V. B., et al.
(författare)
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Temperature limits to deep subseafloor life in the Nankai Trough subduction zone
- 2020
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 370:6521, s. 1230-1234
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Tidskriftsartikel (refereegranskat)abstract
- Microorganisms in marine subsurface sediments substantially contribute to global biomass. Sediments warmer than 40 degrees C account for roughly half the marine sediment volume, but the processes mediated by microbial populations in these hard-to-access environments are poorly understood. We investigated microbial life in up to 1.2-kilometer-deep and up to 120 degrees C hot sediments in the Nankai Trough subduction zone. Above 45 degrees C, concentrations of vegetative cells drop two orders of magnitude and endospores become more than 6000 times more abundant than vegetative cells. Methane is biologically produced and oxidized until sediments reach 80 degrees to 85 degrees C. In 100 degrees to 120 degrees C sediments, isotopic evidence and increased cell concentrations demonstrate the activity of acetate-degrading hyperthermophiles. Above 45 degrees C, populated zones alternate with zones up to 192 meters thick where microbes were undetectable.
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| 2. |
- Rubensson, Jan-Erik, et al.
(författare)
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Influence of the Radiative Decay on the Cross Section for Double Excitations in Helium
- 1999
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 83:5, s. 947-950
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Tidskriftsartikel (refereegranskat)abstract
- The fluorescence yield spectrum of the double excitations in helium has been measured. All three Rydberg series converging to the N = 2 threshold are resolved, and the intensity of the individual lines is determined. The intensity variation through each series indicates that the radiative decay channel cannot be neglected when discussing the double excitations in helium. This calls for a revision of the interpretation of the absorption spectrum, and sets the limit for using the ion yield method to monitor the absorption probability.
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| 3. |
- Felser, C, et al.
(författare)
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Metal valence states in Eu0.7NbO3, EuNbO3, and Eu2Nb5O9 by TB-LMTO-ASA band-structure calculations and resonant photoemission spectroscopy
- 1998
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 57, s. 1510-1514
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structures of Eu2Nb5O9, EuNbO3, and Eu0.7NbO3 have been investigated by photoemission and total-yield spectroscopy with synchrotron radiation, and in the case of Eu2Nb5O9 by tight-binding linear muffin-tin orbital (LMTO) band-structure calculations. A central question for reduced europium niobates is that of the valence of Eu and Nb. Both europium and niobium atoms can appear in different valence states so that various electronic configurations in the title compounds are possible. For this reason, the valence band was studied by the resonant Eu 4d⃗4f technique to determine the Eu valence. The final-state 4f6 multiplet of divalent Eu is dominant in all spectra. Since there are no 4f density of states at the Fermi level, valence fluctuations are not expected. The niobium valence states were investigated by core-level spectroscopy. We found only one 3d5/23d3/2 doublet for the Nb 3d core level in EuNbO3 and Eu0.7NbO3, while in Eu2Nb5O9, two 3d doublets have been observed, corresponding to two chemically distinct niobium atoms in this compound. The 3d5/2 peak in EuNbO3 is assigned to the +4 nominal valence state at a binding energy of 209.7 eV. The doublet of Eu0.7NbO3 is observed at 0.5 eV higher binding energy (at 210.2 eV), which then corresponds to a nominal Nb+4+δ chemical state. In Eu2Nb5O9, the valence of Nb in the NbO6 octahedra is less than +5 and in the Nb6O12 clusters is close to +2 as expected. This is in accordance with the LMTO band-structure calculations
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| 4. |
- Nordgren, J., et al.
(författare)
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Soft x-ray emission spectroscopy using monochromatized synchrotron radiation (invited)
- 1989
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 60:7, s. 1690-1696
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Tidskriftsartikel (refereegranskat)abstract
- Soft x-ray emission spectroscopy is a common tool for the study of the electronic structure of molecules and solids. However, the interpretation of spectra is sometimes made difficult by overlaying lines due to satellite transitions or close-lying core holes. Also, irrelevant inner core transitions may accidentally fall in the wavelength region under study. These problems, which often arise for spectra excited with electrons or broadband photon sources can be removed by using monochromatized synchrotron radiation. In addition, one achieves other advantages as well, such as the ability to study resonant behavior. Another important aspect is the softness of this excitation agent, which allows chemically fragile compounds to be investigated. In this work we demonstrate the feasibility of using monochromatized synchrotron radiation to excite soft x-ray spectra. We also show new results which have been accomplished as a result of the selectivity of the excitation. The work has been carried out using the Flipper I wiggler beamline at HASYLAB in Hamburg using a new grazing incidence instrument designed specifically for this experiment. The photon flux at the Flipper I station (typically 5×1012 photons per second on the sample with a 1% bandpass) is enough to allow soft x-ray fluorescence spectra to be recorded at relatively high resolution and within reasonable accumulation times (typically, the spectra presented in this work were recorded in 30 min). The spectrometer is based on a new concept which allows the instrument to be quite small, still covering a large wavelength range (10-250 Å). The basic idea involves the use of several fixed mounted gratings and a large two-dimensional detector. The grating arrangement provides simple mounting within a limited space and, in particular, large spectral range. The detector can be moved in a three-axis coordinate system in order to cover the different Rowland curves defined by the different gratings. The arrangement permits the use of gratings with different radii, which further facilitate the achievement of optimum performance over a large range. Two-dimensional detection is used to allow a large solid angle, without suffering from loss of resolution due to imaging errors. The detector is based on five 2-in. MCPs with resistive anode read out. The sensitivity of the detector, which is normally very low for soft x rays, especially at grazing angles, is enhanced by CsI coating and by using an entrance electrode.
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| 5. |
- Rubensson, J. E., et al.
(författare)
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Resonant behavior in soft x-ray fluorescence excited by monochromatized synchrotron radiation
- 1988
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Ingår i: Physical Review Letters. - 0031-9007. ; 60:17, s. 1759-1762
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Tidskriftsartikel (refereegranskat)abstract
- Soft x-ray emission spectra of TiN, excited by monochromatized synchrotron radiation, have been recorded in a grazing-incidence spectrometer. The tunability of the excitation energy has allowed the pure N K and Ti LIII emission spectra to be isolated for the first time. A new type of resonance is observed in the Ti L emission spectrum, and interpreted as due to the decay of a quasiatomic intermediate state. The results call for a reinterpretation of Ti L spectra and a revision of the interpretation of 3d-metal L-emission spectra in general.
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| 6. |
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| 7. |
- Wassdahl, N., et al.
(författare)
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Synchrotron-radiation-excited soft-x-ray-fluorescence studies of Cu and Zn : On the validity of the sudden approximation
- 1990
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Ingår i: Physical Review Letters. - 0031-9007. ; 64:23, s. 2807-2810
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Tidskriftsartikel (refereegranskat)abstract
- The L23 x-ray-emission spectra of Cu and Zn have been recorded using tunable-synchrotron-radiation-excited fluorescence spectroscopy. The satellite structure was studied in detail by varying the excitation energy from threshold to several hundred eV above. Strong satellites are observed which can unambiguously be associated with the decay of multiply excited states. This disproves recent claims of a breakdown of the sudden approximation in this regime.
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