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Accurate Transition Probabilities from Large-scale Multiconfiguration...

Jönsson, Per; Godefroid, Michel; Bieron, Jacek; Gaigalas, Gediminas; Brage, Tomas
Publication in Program and Abstracts : Eighth International Conference on Atomic and Molecular Data and Their Applications: ICAMDATA 8; (2012)
Eighth International Conference on Atomic and Molecular Data and Their Applications: ICAMDATA-8 2012, National Institute of Standards and Technology, Washington (USA), September 30 – October 4

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English abstract:

The quality and resolution of solar, stellar, and other types of plasma observations, has so improved that the accuracy of atomic data is frequently a limiting factor in the interpretation of these new observations. An obvious need is for accurate transition probabilities. Laboratory measurements, e.g. using ion/traps, beam-foil or laser techniques, have been performed for isolated transitions and atoms, but no systematic laboratory study exists or is in progress. Instead the bulk of these atomic data must be calculated. Multiconﬁguration methods, either non-relativistic with Breit-Pauli corrections (MCHF+BP) or fully relativistic (MCDHF), are useful to this end. The main advantage of multiconﬁguration methods is that they are readily applicable to excited and openshell systems, including open f-shells, across the whole periodic table, thus allowing for mass production of atomic data. The accuracy of these calculations depends on the complexity of the shell structure and on the underlying model for describing electron correlation. By systematically increasing the number of basis functions in large-scale calculations, as well as exploring different models for electron correlation, it is often possible to provide both transition energies and transition probabilities with some error estimate. The success of the calculations also depends on available computer software. In this talk we will describe a collaborative effort to continue the important and acclaimed work of Prof. Charlotte Froese Fischer and to develop state-of-the-art multiconﬁguration codes. In the latest versions of the non-relativistic (ATSP2K) and relativistic (GRASP2K) multiconﬁguration codes angular integration is performed using second quantization in the coupled tensorial form, angular momentum theory in three spaces (orbital, spin and quasispin), and a generalized graphical technique that allows open f-shells. In addition it is possible to transform results given in the relativistic j j-coupling to the more useful LSJ-coupling. Biorthogonal transformation techniques are implemented and initial and ﬁnal states in a transition can be separately optimized. The main parts of the codes are also adapted for parallel execution using MPI. Results from recent large-scale calculations using these codes will be presented for systems of different complexity. Of special interest are spectrum calculations, where all states up to a certain level are computed at the same time. Finally, we look at new computational developments that allow basis functions in multiconﬁguration methods to be built on several independent and non-orthogonal sets of one-electron orbitals. Initial calculations indicate that the increased ﬂexibility of the orbital sets allows transition energies, as well as other atomic properties, to be predicted to a much higher accuracy than before.

A model for calculation of stress corrosion crack growth
Ståhle, Per; Jivkov, Andrey Conference paper in Configurational mechanics (2004) 5th EUROMECH Solid Mechanics Conference (ESMC 5), 17-22 August 2003, Thessaloniki, Greece	peer-reviewed conference PAPER

English abstract:

As much as 25% of all accidents in process industry reported to the Swedish Plant Inspectorate are caused by stress corrosion crack growth. The situation is believed to be similar in the all industrialised countries. It contributes to the severity of the accidents that they often occurs unexpectedly and at loads that may be far below what normally causes crack growth Experts in the fields of metallurgy, corrosion have treated stress corrosion using mechanical models based on elastic or elastic plastic stress fields where the crack tip is treated as a point. In view of the near tip load distribution this leads to paradoxic results. In the present model corrosion is forming the geometry of the crack tip and is thus itself creating the conditions for strain concentration. We incorporate an interaction between electro-chemical processes and the deformation of the crack tip region in a fracture mechanical theory. The model is based on material dissolution simply being proportional to the surface stretch. No crack growth criteria is used. Computation of the mechanical state is based on a finite element formulation for large strains. The formation of a crack from a surface depression via a pit is studied. Low frequency cyclic load is considered. At the end of a load cycle a metal oxide compound is growing on the crack surface. We assume that there is sufficient time for the chemical process to form a protective film that fully covers the crack surface. This temporarily interrupts the corrosion process. During the application of next load cycle the stretch of the surface breaks the protective film. This creates gaps in the film, which allow dissolution of the underlaying metal. The chemical environment of the crack tip is assumed to be constant and unaffected by the changing geometry as the crack is developing. We assume that there is a linear relationship between strain and corrosion rate, in the sense of removed material per unit of area during each load cycle. The model simulates how dissolution lead to surface roughness, how pits form and grow to become cracks in one continuous process. The resulting natural variation of lengths of the formed cracks causes the cracks to grow with different speeds. During continuation one crack after the other falls into a wake behind a larger crack. Thus, crack tip load of the smaller decreases and finally causes crack arrest: At the end of the simulation only one growing crack remains. The results are compared with experimental observations.

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Achieving services when turning a waybill into an e-waybill
Bakhtyar, Shoaib; Persson, Jan A.; Holmgren, Johan : European Commission (2011) International Conference on Paperless Freight Transport Logistics. 10-11 May 2011, Munich, Germany	conference PAPER

Affine Structure from Translational Motion in Image Sequences
Hammarstedt, Pär; Kahl, Fredrik; Heyden, Anders Conference paper in Lecture Notes in Computer Science (2003) Scandinavian Conference on Image Analysis, Gothenburg, Sweden	peer-reviewed conference PAPER

Analysis of a Loosely Supported Beam Under Harmonic Excitations
Knudsen, J.; Massih, Ali R : Pettigrew, M.J. (1999) Flow-induced vibration 1999: presented at the 1999 ASME Pressure Vessels and Piping Conference, Boston, Massachusetts, August 1-5, 1999, pricipal editor M.J. Pettigrew. Serie: PVP, 99-0304524-7; 389	peer-reviewed conference PAPER

Analysis of a Loosely Supported Beam Under Random Excitations
Knudsen, J; Massih, Ali R; Gupta, R Conference paper in Proceedings of 7th International Conference Flow-Induced Vibration (FIV2000) (2000)	peer-reviewed conference PAPER