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Sökning: WFRF:(Markenroth Bloch Karin)

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  • Aleksandrov, D, et al. (författare)
  • Halo excitations in fragmentation of He-6 at 240 MeV/u on carbon and lead targets
  • 2000
  • Ingår i: Nuclear Physics A. - 0375-9474. ; 669:1-2, s. 51-64
  • Tidskriftsartikel (refereegranskat)abstract
    • Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while the dipole mode is dominating in Coulomb dissociation. Neither theoretically predicted new resonance states in He-6 nor nuclear excitation of a dipole mode were found. Direct evidence has been obtained for strong suppression of Coulornb post-acceleration in direct Coulomb breakup in a lead target.
  • Chulkov, L V, et al. (författare)
  • Three-body correlations in electromagnetic dissociation of Borromean nuclei: The He-6 case
  • 2005
  • Ingår i: Nuclear Physics A. - 0375-9474. ; 759:1-2, s. 23-42
  • Tidskriftsartikel (refereegranskat)abstract
    • Dissociation of He-6 on a lead target has been studied at 240 MeV/u. The four-momenta of the two neutrons in coincidence with alpha-particles have been measured and used to reconstruct the three-body energy and angular correlations in the final state. For the first time, three-body correlations were included in the analysis of the He-6 dissociation data, and compared with calculations assuming a dipole mode for the electromagnetic dissociation. In addition, the experimental data have been analyzed using a series expansion of the final transition amplitude into hyperspherical functions, showing the importance of both nn and alpha n final-state interactions. It is shown that the dissociation process is governed by a transition of one neutron from the p-shell in the 6He ground state to the s-shell in the continuum further indicating that the role of the transition through an intermediate He-5(3/2(-)) state is more important than expected. (c) 2005 Elsevier B.V. All rights reserved.
  • Axelsson, L., et al. (författare)
  • Study of the unbound nucleus 11N by elastic resonance scattering
  • 1996
  • Ingår i: Physical Review C (Nuclear Physics). - American Physical Society. - 0556-2813. ; 54:4, s. 1511-1514
  • Tidskriftsartikel (refereegranskat)abstract
    • Resonances in the unbound nucleus 11N have been studied, using the resonance scattering reaction 10C+p. The data give evidence for three states above the 10C+p threshold with energies 1.30, 2.04, and 3.72 MeV. These states can be interpreted, in a potential-model analysis, as the ground state and the first two excited states with spin-parity 1 / 2+, 1 / 2-, and 5 / 2+ arising from the shell-model orbitals 1s1 / 2, 0p1 / 2, and 0d5 / 2. A narrow state superposed on a broad structure found at higher energy could be interpreted as the mirror state of the 3 / 2- in 11Be shifted down in energy. This shift would suggest a large radius of the potential.
  • Bergmann, U.C., et al. (författare)
  • Light exotic isotopes: recent beam developments and physics applications at ISOLDE
  • 2002
  • Ingår i: Nuclear Physics, Section A. - Elsevier. - 0375-9474. ; 701:1-4, s. 363-368
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper is divided in three parts: (i) the measurement of yields and decay losses of Li and Be isotopes released from a thin foil tantalum target at the CERN/ISOLDE PS-Booster; (ii) results from β-decay experiments on 12Be and 14Be, an improved half-life of 21.49(3) ms has been obtained for 12Be; (iii) the β-decay of 9C. An outline of the analysis procedure to determine the branching at high excitation energies is given. The ground-state branch has been determined to 54.1(15)%.
  • Bergmann, U C, et al. (författare)
  • New information on b-delayed neutron emission from 12,14Be
  • 1999
  • Ingår i: Nuclear Physics, Section A. - Elsevier. - 0375-9474. ; 658:2, s. 129-145
  • Tidskriftsartikel (refereegranskat)abstract
    • The β-delayed neutron branches from neutron-rich Be-isotopes have been measured with a setup sensitive down to thermal energies. For 14Be a new value of Pn = 101 ± 4% has been found for the total neutron-emission probability and an upper limit of 2.4% (95% confidence level) is imposed on the combination P2n + 3P3n of multi-neutron emission probabilities. Moreover, an improved value of Pn = 0.50 ± 0.03% has been obtained for 12Be. A time-correlation method, previously developed for a continuous radioactive beam to determine neutron branching ratios, has been revised and adapted to the pulsed secondary beam at ISOLDE, CERN.
  • Bergmann, U.C., et al. (författare)
  • On the b-decay of 9C
  • 2001
  • Ingår i: Nuclear Physics A. - Elsevier. ; 692:3-4, s. 427-450
  • Tidskriftsartikel (refereegranskat)abstract
    • In β-decay experiments on 9C at CERN/ISOLDE the β-strength was determined to the ground state, the 12.2 MeV excited state and the Isobaric Analog State (IAS) at 14.655 MeV in 9B. A large β-strength asymmetry is deduced for the mirror transitions of 9C and 9Li to states around 12 MeV excitation energy. A satisfactory description of the three-body decay from a narrow energy region around the 12.2 MeV resonance is obtained within a sequential model involving the ground and first-excited states of 5Li and 8Be. From the study of angular correlations the spin of the 12.2 MeV state is determined as 5/2−. For the first time the population of the IAS is observed in β-decay and new information on the decay of this state is obtained. The advantages of a closely packed, highly segmented detector setup are demonstrated.
  • Bergvall, Erik, et al. (författare)
  • Regularization of phase contrast magnetic resonance images using optical flow and smoothness constraints
  • 2005
  • Ingår i: Computers in Cardiology, 2005,Lyon, France,2005-09-25 - 2005-09-28. - IEEE - Institute of Electrical and Electronics Engineers Inc..
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents a post processing strategy for myocardial velocity fields obtained by phase contrast magnetic resonance imaging. Such data can be used to track cardiac motion and to calculate strain. The method combines data regularization with optical flow estimation to overcome the partial volume effect in the image acquisition. Validation is performed both in vitro and in vivo and it is shown that the method improves the accuracy of cardiac motion tracking.
  • Bergvall, Erik, et al. (författare)
  • Spline-based cardiac motion tracking using velocity-encoded magnetic resonance imaging.
  • 2008
  • Ingår i: IEEE Transactions on Medical Imaging. - IEEE - Institute of Electrical and Electronics Engineers Inc.. - 1558-254X. ; 27:8, s. 1045-1053
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper deals with the problem of tracking cardiac motion and deformation using velocity-encoded magnetic resonance imaging. We expand upon an earlier described method and fit a spatiotemporal motion model to measured velocity data. We investigate several different spatial elements both qualitatively and quantitatively using phantom measurements and data from human subjects. In addition, we also use optical flow estimation by the Horn-Schunk method as complementary data in regions where the velocity measurements are noisy. Our results show that it is possible to obtain good motion tracking accuracy in phantoms with relatively few spatial elements, if the type of element is properly chosen. The use of optical flow can correct some measurement artifacts but may give an underestimation of the magnitude of the deformation. In human subjects the different spatial elements perform quantitatively in a similar way but qualitative differences exists, as shown by a semiquantitative visual scoring of the different methods.
  • Björkman-Burtscher, Isabella M., et al. (författare)
  • Detailed anatomy at 7T
  • 2017
  • Ingår i: Neuroimaging : Anatomy Meets Function - Anatomy Meets Function : Anatomy Meets Function. - Springer International Publishing. - 9783319574264 - 9783319574271 ; s. 69-80
  • Bokkapitel (refereegranskat)
  • Bock, Jelena, et al. (författare)
  • Validation and reproducibility of cardiovascular 4D-flow MRI from two vendors using 2 × 2 parallel imaging acceleration in pulsatile flow phantom and in vivo with and without respiratory gating
  • 2018
  • Ingår i: Acta Radiologica. - SAGE Publications. - 0284-1851.
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: 4D-flow magnetic resonance imaging (MRI) is increasingly used. Purpose: To validate 4D-flow sequences in phantom and in vivo, comparing volume flow and kinetic energy (KE) head-to-head, with and without respiratory gating. Material and Methods: Achieva dStream (Philips Healthcare) and MAGNETOM Aera (Siemens Healthcare) 1.5-T scanners were used. Phantom validation measured pulsatile, three-dimensional flow with 4D-flow MRI and laser particle imaging velocimetry (PIV) as reference standard. Ten healthy participants underwent three cardiac MRI examinations each, consisting of cine-imaging, 2D-flow (aorta, pulmonary artery), and 2 × 2 accelerated 4D-flow with (Resp+) and without (Resp−) respiratory gating. Examinations were acquired consecutively on both scanners and one examination repeated within two weeks. Volume flow in the great vessels was compared between 2D- and 4D-flow. KE were calculated for all time phases and voxels in the left ventricle. Results: Phantom results showed high accuracy and precision for both scanners. In vivo, higher accuracy and precision (P < 0.001) was found for volume flow for the Aera prototype with Resp+ (–3.7 ± 10.4 mL, r = 0.89) compared to the Achieva product sequence (–17.8 ± 18.6 mL, r = 0.56). 4D-flow Resp− on Aera had somewhat larger bias (–9.3 ± 9.6 mL, r = 0.90) compared to Resp+ (P = 0.005). KE measurements showed larger differences between scanners on the same day compared to the same scanner at different days. Conclusion: Sequence-specific in vivo validation of 4D-flow is needed before clinical use. 4D-flow with the Aera prototype sequence with a clinically acceptable acquisition time (<10 min) showed acceptable bias in healthy controls to be considered for clinical use. Intra-individual KE comparisons should use the same sequence.
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