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Träfflista för sökning "WFRF:(Jones I) ;srt2:(2000-2004)"

Sökning: WFRF:(Jones I) > (2000-2004)

  • Resultat 31-40 av 63
  • Föregående 123[4]567Nästa
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31.
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32.
  • Coutinho, J., et al. (författare)
  • Interstitial carbon-oxygen center and hydrogen related shallow thermal donors in Si
  • 2002
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:1, s. 014109-11
  • Tidskriftsartikel (refereegranskat)abstract
    • The interstitial carbon-oxygen defect is a prominent defect formed in e-irradiated Cz-Si containing carbon. Previous stress alignment investigations have shown that the oxygen atom weakly perturb the carbon interstitial but the lack of a high-frequency oxygen mode has been taken to imply that the oxygen atom is severely affected and becomes overcoordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts give further evidence for oxygen overcoordination. Moreover, we find that the calculated stress-energy tensor and energy levels are in good agreement with experimental values. The complexes formed by adding both single (CiOiH) and a pair of H atoms (CiOiH2), as well as the addition of a second oxygen atom, are considered theoretically. It is shown that the first is bistable with a shallow donor and deep acceptor level, while the second is passive. The properties of CiOiH and CiO2iH are strikingly similar to the first two members of a family of shallow thermal donors that contain hydrogen.
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33.
  • Coutinho, J., et al. (författare)
  • Over-coordinated oxygen in the interstitial carbon-oxygen complex
  • 2001
  • Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 305-308
  • Tidskriftsartikel (refereegranskat)abstract
    • The interstitial carbon-oxygen complex is one of the most prominent defects formed in e-irradiated Cz-Si containing carbon. Stress alignment investigations have shown that the oxygen atom only perturbs the carbon interstitial but the lack of a high frequency oxygen mode has been taken to imply that the oxygen atom is over-coordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts, along with the piezoscopic stress-energy tensor support the trivalent model, thus providing evidence for oxygen over-coordination.
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34.
  • Coutinho, J., et al. (författare)
  • Thermal double donors and quantum dots
  • 2001
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87:23, s. 235501-
  • Tidskriftsartikel (refereegranskat)abstract
    • Combined local mode spectroscopy and ab initio modeling are used to demonstrate for the first time that oxygen atoms in thermal double donors (TDD) in Si are in close proximity. The observed vibrational modes in 16O, 18O, and mixed isotopic samples are consistent with a model involving [110] aligned oxygen chains made up of an insulating core lying between electrically active ends. The model also explains the minute spin density observed on oxygen in TDD+ as well as the piezospectroscopic tensors of the donors. The analogy between the thermal donors and quantum dots is emphasized.
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35.
  • Drakare, Stina, 1969- (författare)
  • The Role of Picophytoplankton in Lake Food Webs
  • 2002
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Picophytoplankton were inferior competitors for inorganic phosphorus compared to heterotrophic bacteria. This may be due to the source of energy available for the heterotrophs, while cell-size was of minor importance. However, picophytoplankton were superior to large phytoplankton in the competition for nutrients at low concentrations. Biomass of picophytoplankton was low in brownwater lakes and high in clearwater lakes, compared to the biomass of heterotrophic bacteria. The results suggest that picophytoplankton are inferior to heterotrophic bacteria in the competition for inorganic nutrients in brownwater lakes, where the production of heterotrophic bacteria is subsidized by humic dissolved organic carbon (DOC) Relative to large phytoplankton, picophytoplankton were most important in lakes with intermediate water colour, despite the fact that the lowest nutrient concentrations were found in the clearwater lakes. Large phytoplankton in the clearwater lakes may be able to overcome nutrient competition with picophytoplankton by vertical migration.In conclusion, changes in nutrient content, light availability and concentrations of DOC affect the interactions of heterotrophic bacteria, picophytoplankton and large phytoplankton and are therefore important factors for the structure of the food web in the pelagic zones of lakes.Picophytoplankton (planktonic algae and cyanobacteria, < 2 µm) constitute an important component of pelagic food webs. They are linked to larger phytoplankton and heterotrophic bacteria through complex interactions including competition, commensalism and predation. In this thesis, field and laboratory studies on the competitive ability of picophytoplankton are reported.
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36.
  • Fynbo, H. O. U., et al. (författare)
  • News on C-12 from beta-decay studies
  • 2004
  • Ingår i: Nuclear Physics A. - 0375-9474. ; 738, s. 59-65
  • Konferensbidrag (refereegranskat)abstract
    • We discuss the importance of the spectroscopic properties of the resonances of C-12 just above the 3alpha-threshold, and review the existing experimental information of this region with emphasis on 0(+) and 2(+) states. A new experimental approach for studying the beta-decays of B-12 and N-12 is presented based on techniques developed in the context of Radioactive beam (rare isotope) physics. Finally preliminary results from an ongoing analysis of two recent experiments are given.
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37.
  • Gayou, O, et al. (författare)
  • Measurement of G(Ep)/G(Mp) in (e)over-right-arrowp -> e(p)over-right-arrow to Q(2)=5.6 GeV2
  • 2002
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114. ; 88:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The ratio of the electric and magnetic form factors of the proton G(Ep)/G(Mp), which is an image of its charge and magnetization distributions, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic (e) over right arrowp --> e (p) over right arrow reaction. The new data presented span the range 3.5 < Q(2) < 5.6 GeV2 and are well described by a linear Q(2) fit. Also, the ratio rootQ(2) F-2p/F-1p reaches a constant value above Q(2) = 2 GeV2.
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38.
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39.
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40.
  • Goss, J.P., et al. (författare)
  • First principles studies of H in diamond
  • 2001
  • Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 186:2, s. 263-8
  • Tidskriftsartikel (refereegranskat)abstract
    • Ab initio methods are used to investigate hydrogen defects in diamond. For the isolated impurity, the bond-centered site is found lowest in energy and posses both donor and acceptor levels. The neutral defect possesses a single local mode with very small infrared effective charge, but the effective charge for the negative charge state is much larger. H+ is calculated to be very mobile with a low activation barrier. Hydrogen dimers are stable as H*2 defects which are also found to be almost IR-inactive. The complex between B and H is investigated and the activation energy for the reaction B-H → B - + H+ found to be in rasonable agreement with experiment. Hydrogen is strongly bound to dislocations which, together with H*2, may form part of the hydrogen accumulation layer detected in some plasma studies.
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