| 1. |
- Aalto, Susanne, 1964
(författare)
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Molecular Clouds in Starburst Galaxies
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Starbursts in the centres of galaxies are believed to be caused by funneling of gas towards the inner regions. Gravitational interactions between galaxies are known to cause vast rearrangements of their structure as well as induce bursts of star formation in their nuclear regions. However, radial gas-transport may also be the result of a bar- instability intrinsic to the system. This report deals with the effect of a starburst on the molecular medium of galaxies. The mm-wave, rotational transitions of interstellar molecules serve as probes of the physical conditions, kinematics and total mass of the molecular gas. Observations of the J=1-0, J=2-1 and J=3-2 transitions of 12Co, the J=1-0 and J=2-1 transitions of 13Co, the J=1-0 transitions of C180 and HCN and the J=2-1 transition of CS are used to determine the properties of the molecular gas in starbursting and normal galaxies. The mean escape probability approximation is used to solve the radiative transfer equations. The inferred properties of the molecular clouds in the centres of starburst galaxies differ from those of Galactic disk clouds. Such a deviation is likely to be induced by a central gas concentration and/or the nuclear starburst disrupting the clouds. Large 12CO/13CO J=1-0 intensity ratios (R>20) are measured towards luminous mergers implying unusual, high-pressure, molecular cloud ensembles. Model cloud ensembles for the merging system, NGC 3256, and the starburst spiral NGC 1808 suggest that the 12CO-emission is dominated by warm (Tk = 100 - 300 K), small (0.5-1 pc) and moderately dense (n = 2 - 7 x 103 cm-3) molecular clouds. Such temperatures and densities are typical of Galactic photon dominated regions (PDRs). Statistical studies of molecular line ratios towards galaxy centres indicate that the optical depth of the 12CO 1-0 emission is moderate, .tau.Ã? 1. Many starburst galaxies have large-scale excitation gradients indicating warm, dense gas in the centre, and normal cool molecular gas in their extended disks. NGC 3256, in particular, has a large R = 35 in the centre, while it is found to be only R = 10 - 15 at positions 43" off centre. The model cloud ensemble of NGC 1808 indicate that the 12CO-emitting gas may be diffuse rather than self-gravitating, this could be a common phenomenon in starburst galaxies.
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| 2. |
- Aardal, Karen, et al.
(författare)
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On the resemblance between the Kornai-Liptak and cross decomposition techniques for block-angular linear programs
- 1990
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Ingår i: European Journal of Operational Research. - : Elsevier BV. - 0377-2217 .- 1872-6860. ; 46:3, s. 393-398
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the resemblance is demonstrated between the master- and subproblems generated by the Kornai-Liptak algorithm and the subproblems obtained by using the cross decomposition method on linear optimization problems with block-angular structure. The significance of the similarity between these two algorithms becomes apparent considering the main disadvantage attributed to cross decomposition. In cross decomposition a master problem has to be solved from time to time since the subproblems alone do not always give a converging sequence of primal and dual solutions. But if the cross decomposition algorithm is modified in such a way that the successive primal and dual subproblem solutions are taken into consideration with equal weights, this results in the Kornai-Liptak algorithm for which convergence is guaranteed
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| 3. |
- Aas, Gro Hanne
(författare)
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Kvinneforskningspolitiske (pr)øvelser
- 1999
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Målsettingen for licentiatuppsatsen er å analysere nordisk kvinneforsknings formuleringer av forskningspolitiske felter, problemstillinger og utfordringer, og gjennom kontakt og diskusjon bidra til samarbeid, diskusjoner og offentlighet om forskingspolitikk i kvinneforskning. Arbeidet har tatt utgangspunkt i relativt nytt materiale fra Danmark, Norge og Sverige. I kap. 1 presenteres prosjektet, problemstillinger og materiale. Kapitlene 2-6 består av innledninger og artikler holdt eller skrevet i løpet av de to senaste åren. Diskusjoner om kjønn og akademia står i fokus i kap. 2 - "Universities have politics". I kap. 3, artikkelen "Gamle og nye drømmer", diskuteres et kvinneforskningspolitiske intervensjonsprosjekt som blev utført for en del år tilbake, og det antydes noen nye omdreiningspunkter for et slikt arbeid. Enkelte perspektiver utdypes i kap. 4, "Kvinneforskningens samfunnskontrakt", hvor termen "kvinneperspektiv" som forskningspolitisk term granskas krtitiskt. De to siste kapitlene tar utgangspunkt i den norske forskningsmeldingen som kom våren 1999. Ut fra tre lesestrategier forsøkes det leses muligheter for kvinneforskningspolitiske strategier. Det ses også på innholdet i regjeringens forskningspolitiske verdidebatt, og det diskuteres mulige intervensjoner i denne ut fra feministiske vitenskaps- og teknologistudier.
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| 4. |
- Abarkan, Abdellah, 1960
(författare)
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Bebyggelsemönster i medelhavsområdet: en studie av medinan i Fes ställd i relief mot Siena|
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is an analysis and comparative study of medieval Mediterranean urban patterns. With urban patterns is meant the arrangement of houses and public spaces with special regard to the relations between them. The thesis contains four parts. Previous research on Muslim cities is described and commented in the first part. A difference between research before and after 1960 is noted. The Medina of Fes is discussed in the second part. In an historical background sketch the foundation of the Medina and its development are presented. The spatial analysis shows that the physical structure of the Medina is based on a primary pattern unit of a square courtyard house with a closed, inward-turned physical structure. A number of these primary units are grouped around a cul de sac to form a second-level community unit; a number of these latter form a quarter. The quarters are adjacent and close to each other which means that the Medina as a whole can be regarded as a complex physical and social unit surrounded with the city walls. In a comparable approach the physical and social structure of Siena is studied. The primary units here are the casa corte, which is similar to the courtyard of the Medina, and the casa a schiera which is a filehouse without any comparative physical form in the medina. These two different primary units engendered two types of building patterns, one in the city centre where courtyard units are grouped around a central square, and the other one in the periphery of the city formed by the alignment of the filehouses along the street. An attempt to compare the physical and social units in the Medina and Siena is made in the fourth part of this thesis. The primary units, the community units, the quarters and the cities are compared. This comparative study shows that the similarities between the Medina and Siena are much more apparent on the social level and on the level of the smaller physical units, i.e. the habitat, than between the larger social and physical composition of the quarters.
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| 5. |
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| 6. |
- Abdulwahab, Fethi, 1964
(författare)
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Postprocessing Techniques and Adaptivity in the Finite Element Method
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Finite Element (FE) method is an approximate method and as such the accuracy of its solutions must be controlled to allow for a reliable application. This thesis deals with error estimation and improvements of the FE solutions based on superconvergent properties of the FE solution in certain points. Two new postprocessing procedures are developed for elliptic problems. The procedures are based on local patches of elements and developed in such a way that the methods function at local level. Being local methods, the cost involved in implementing the procedures is small. The derivatives of the FE solutions are discontinuous across element boundaries. The primary purpose of the proposed postprocessing procedures is to smooth the discontinuous derivatives of finite element solutions like stresses and fluxes. The smoothed solution is used both as a new improved solution and in an error estimation. The presented postprocessing methods do not only smooth the stress discontinuities but also improve the satisfaction of the governing differential equation. This is in contrast to the fact that the FE solutions fulfill equilibrium conditions only in a weak and global sense. Similarly, the FE solutions do not generally satisfy the prescribed natural boundary conditions satisfactorily. On the other hand, the solutions obtained by the proposed postprocessing procedure satisfy the prescribed boundary conditions. Satisfaction of both the equilibrium and boundary conditions is achieved in the sense of the least squares. The proposed methods yield superconvergent solutions meaning that the accuracy of the postprocessed solutions are at least one order higher than the finite element solutions. This in its turn means that use of these postprocessed solutions in error estimations gurantees that the error estimate is asymptotically exact or that the estimated discretization error converges towards the true error in the limit. Several numerical test examples are given to validate the accuracy and effectiveness of these new methods. The presented methods are also implemented in an adaptive finite element procedure of the h-version or mesh enrichment. The postprocessing procedures proposed in this thesis can be regarded as a step forward towards an accurate and automated adaptive analysis in which the ultimate goal is to provide finite element solutions of high quality in an economical manner. Starting from some arbitrary mesh, such an automated adaptive procedure should provide an improved finite element model that meets a user specified level of accuracy. To accomplish this goal, every FE program package should be equipped with efficient postprocessing procedures.
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| 7. |
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| 8. |
- Aberg, Jan, et al.
(författare)
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Multialphabet coding with separate alphabet description
- 1997
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Ingår i: Proceedings. Compression and Complexity of SEQUENCES 1997. - 0818681322 ; , s. 56-65
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Konferensbidrag (refereegranskat)abstract
- For lossless universal source coding of memoryless sequences with an a priori unknown alphabet size (multialphabet coding), the alphabet of the sequence must be described as well as the sequence itself. Usually an efficient description of the alphabet can be made only by taking into account some additional information. We show that these descriptions can be separated in such a way that the encoding of the actual sequence can be performed independently of the alphabet description, and present sequential coding methods for such sequences. Such methods have applications in coding methods where the alphabet description is made available sequentially, such as PPM.
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| 9. |
- Aberg, J., et al.
(författare)
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Towards understanding and improving escape probabilities in PPM
- 1997
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Ingår i: Proceedings DCC '97. Data Compression Conference. - 0818677619 ; , s. 22-31
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Konferensbidrag (refereegranskat)abstract
- The choice of expressions for the coding probabilities in general, and the escape probability in particular, is of great importance in the family of PPM algorithms. We present a parameterized version of the escape probability estimator which, together with a 'compactness' criterion, provides guidelines for the estimator design given a 'representative' set of files. This parameterization also makes it possible to adapt the expression of the escape probability during one-pass coding. Finally, we present results for one such compression scheme that illustrates the usefulness of our approach.
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| 10. |
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