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| 5. |
- Dias, E.W.B, et al.
(författare)
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Breakdown of the independent particle approximation in high-energy photoionization
- 1997
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Ingår i: Physical Review Letters. - 0031-9007. ; 78:24, s. 4553-4556
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Tidskriftsartikel (refereegranskat)abstract
- The independent particle approximation is shown to break down for the photoionization of both inner and outer nl (l > 0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed.
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| 6. |
- Hemmers, O, et al.
(författare)
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Beyond the dipole approximation: angular-distribution effects in valence photoemission
- 1997
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - 0953-4075. ; 30:21, s. L727-L733
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Tidskriftsartikel (refereegranskat)abstract
- Angular distributions of valence photoelectrons showing effects due to highermultipole photon interactions have been measured for the first time. Neon 2s and 2p photoemission exhibits effects beyond the dipole approximation throughout the 250 to 1200 eV photon-energy range studied. The results suggest that any photoemission experiment, on any sample, can be affected at relatively low photon energies, pointing to a general need for caution in interpreting angle-resolved-photoemission measurements.
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| 9. |
- Marques, F. M., et al.
(författare)
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Neutrons from the breakup of C-19
- 1996
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 381:4, s. 407-412
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Tidskriftsartikel (refereegranskat)abstract
- Neutrons arising from the breakup of a 30 MeV/nucleon C-19 beam on a tantalum target have been measured using the 98 element array DEMON. A narrow, forward peaked neutron angular distribution, with a corresponding momentum spread considerably smaller than those measured simultaneously for N-21, O-22 and F-24 was observed for charged fragments with Z
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| 11. |
- Kiorboe, T., et al.
(författare)
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Intensive aggregate formation with low vertical flux during an upwelling-induced diatom bloom
- 1998
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Ingår i: Limnology and Oceanography. - 0024-3590. ; 43:1, s. 104-116
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Tidskriftsartikel (refereegranskat)abstract
- The surfaces of most pelagic diatoms are sticky at times and may therefore form rapidly settling aggregates by physical coagulation. Stickiness and aggregate formation may be particularly adaptive in upwelling systems by allowing the retention of diatom populations in the vicinity of the upwelling center. We therefore hypothesized that upwelling diatom blooms are terminated by aggregate formation and rapid sedimentation. We monitored the development of a maturing diatom (mainly Chaetoceros spp.) bloom in the Benguela upwelling current during 7 d in February. Chlorophyll concentrations remained consistently high during the observation period (similar to 500 mg Chi m(-2)) and phytoplankton grew at an average specific rate of 0.25 d(-1). The diatoms were extraordinarily sticky, with stickiness coefficients of up to 0.40, which is the highest ever recorded for field populations. Combined with estimates of turbulent shear in the ocean such stickiness coefficients predict very high specific coagulation rates (0.3 d(-1)). In situ video observation demonstrated the occurrence of abundant diatom aggregates with surface water concentrations between 1,000 and 3,000 ppm. Despite the very high concentration of aggregates, vertical fluxes of phytoplankton were very low, with fractional losses <0.005 d(-1), and the aggregates thus seemed to be near neutrally buoyant. Losses due to copepod grazing were also low (similar to 0.025 d(-1)). Most of the aggregates were colonized by the heterotrophic dinoflagellate Noctiluca scintillans that feed upon diatoms in the aggregates. The system appeared to be in near steady state; specific diatom growth rate, coagulation rate, and loss rate due to N, scintillans feeding were all of the same magnitude (0.25-0.3 d(-1)) and the latter two varied in concert. Our observations provide only partial support for the population retention hypothesis because aggregate buoyancy and N, scintillans grazing efficiently reduced the vertical flux of aggregates in this system.
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| 13. |
- Proff, S, et al.
(författare)
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Electromagnetic polarizabilities of nucleons bound in 40Ca, 16O and 4He
- 1999
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Ingår i: Nuclear Physics A. - 0375-9474. ; 646:1, s. 67-82
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Tidskriftsartikel (refereegranskat)abstract
- Differential cross sections for elastic scattering of photons have been measured for 40Ca at energies of 58 and 74 MeV and for 16O and 4He at 61 MeV, in the angular range from 45° to 150°. Evidence is obtained that there are no significant in-medium modifications of the electromagnetic polarizabilities except for those originating from meson exchange currents.
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- Stolte, W.C., et al.
(författare)
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The K-shell Auger decay of atomic oxygen
- 1997
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - 0953-4075. ; 30:20, s. 4489-4497
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Tidskriftsartikel (refereegranskat)abstract
- Relative photoionization cross sections for O+ and O2+ produced by the Auger decay of a 1s hole in atomic oxygen were measured by using synchrotron radiation between 525 and 553 eV. Energies and quantum defects of the members of the two Rydberg series converging to [1s]2s22p4(4P) and [1s]2s22p4(2P) ionization thresholds were determined. In addition, the 2P and 4P ionization thresholds were calculated from the two Rydberg series. The 182 meV resolution of the monochromator allowed a detailed study over both thresholds revealing evidence for post-collision interaction and allowing a comparison of the ionization continuum above both 2P and 4P thresholds with that of the ionization continuum above the Ar L2 and L3 edges. This comparison indicates that the lifetimes of the Ar(2p) and O(1s) hole states are approximately the same.
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