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133. |
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134. |
- Aleksandrov, D., et al.
(author)
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Invariant mass spectrum and alpha-n correlation function studied in the fragmentation of He-6 on a carbon target
- 1998
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In: Nuclear Physics A. - 0375-9474. ; 633:2, s. 234-246
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Journal article (peer-reviewed)abstract
- Momentum distributions and invariant mass spectra from the breakup of He-6 ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 resonance. The shape of the (alpha+n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J(pi) = 3/2(-) resonance. However, no evidence for correlations between cu particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance. (C) 1998 Elsevier Science B.V.
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135. |
- Alén, Claes, 1949
(author)
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On Probability in Geotechnics. Random Calculation Models Exemplified on Slope Stability Analysis and Ground-Superstructure Interaction
- 1998
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Doctoral thesis (other academic/artistic)abstract
- The thesis deals with uncertainty in calculation modelling. Emphasis is put on the design state. Design is a chain of decisions under uncertainty. A probabilistic approach is used to describe the uncertainty and calculations as a way to reveal the uncertainty. Thus, a calculation method becomes an operative tool in a risk analysis, not merely a verification of a prescribed minimum level. The work is a combination of elements from three different academic disciplines; geotechnics, structural mechanics and statistics. Different aspects from two fields of geotechnical modelling are discussed; slope stability as an example of ultimate limit state problems, and interaction ground /superstructure as an example of serviceability limit state problems. For the mathematical solution different algorithms are used; mathematical analysis, point estimate method, Monte-Carlo simulation and reliability analysis. Soil properties are described as random variables. Different uncertainties are accounted for; natural variations, systematic testing errors, random testing errors and errors due to limited testing. Pre-knowledge and test results are combined systematically using Bayesian statistics. Three different levels of complexity of both slope stability analysis and ground/superstructure interaction are given. In both cases, structural models of the soil are given for the third level. For a slope a constant degree of mobilisation is not a prerequisite. Instead the deformation properties of the soil are considered. In the interaction analysis the soil is described as a continuous shear beam on elastic supports. The structural model of the soil can be calibrated against a more rigorous geotechnical model. To determine volumetric creep deformations in clay a simple creep model is presented, in which the soil deformations can be determined as a sum of elastic/plastic deformations and creep deformations.
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