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- 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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| 2. |
- Abbas, Abdul-Karim, 1959, et al.
(författare)
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Bicarbonate-sensitive cysteine induced elevation of extracellular aspartate and glutamate in rat hippocampus in vitro
- 1997
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Ingår i: Neurochemistry International. - 0197-0186. ; 30:3, s. 253-259
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Tidskriftsartikel (refereegranskat)abstract
- The effect of different concentrations of cysteine (0.125, 0.25, 0.5 and 1 mM) on the net efflux of endogenous amino acids was studied by the incubation of rat hippocampal slices. Addition of cysteine (1 mM) in bicarbonate containing low K+ medium (5 min) selectively increased the basal net efflux of glutamate and aspartate by 370% and 396%, respectively. High K+ media (50 mM) containing cysteine (1 mM) evoked the net efflux of glutamate and aspartate by 1 454% and 1 019%, respectively. The corresponding effects in control slices without cysteine were 669% and 404%, respectively. No changes were observed on the concentrations of GABA, glutamine and taurine. The cysteine oxidation products, cysteine sulfinate (0.5 μM) and cystine (0.25 mM) were without effects. The effect of cysteine (0.5 mM) was dramatically reduced in media with no added bicarbonate/CO2. Thus, cysteine in a bicarbonate-sensitive manner selectively increases the extracellular concentration of excitotoxic amino acids in adult rat brain in vitro, possibly by interfering with the carrier-mediated glutamate uptake/ release
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| 4. |
- 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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| 6. |
- Abel, Frida, 1974, et al.
(författare)
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Gain of chromosome arm 17q is associated with unfavourable prognosis in neuroblastoma, but does not involve mutations in the somatostatin receptor 2(SSTR2) gene at 17q24.
- 1999
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Ingår i: British journal of cancer. - : Springer Science and Business Media LLC. - 0007-0920 .- 1532-1827. ; 81:8, s. 1402-9
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Tidskriftsartikel (refereegranskat)abstract
- Deletion of chromosome arm 1p and amplification of the MYCN oncogene are well-recognized genetic alterations in neuroblastoma cells. Recently, another alteration has been reported; gain of the distal part of chromosome arm 17q. In this study 48 neuroblastoma tumours were successfully analysed for 17q status in relation to known genetic alterations. Chromosome 17 status was detected by fluorescence in situ hybridization (FISH). Thirty-one of the 48 neuroblastomas (65%) showed 17q gain, and this was significantly associated with poor prognosis. As previously reported, 17q gain was significantly associated with metastatic stage 4 neuroblastoma and more frequently detected than both deletion of chromosome arm 1p and MYCN amplification in tumours of all stages. 17q gain also showed a strong correlation to survival probability (P = 0.0009). However, the most significant correlation between 17q gain and survival probability was observed in children with low-stage tumours (stage 1, 2, 3 and 4S), with a survival probability of 100% at 5 years from diagnosis for children with tumours showing no 17q gain compared to 52.5% for those showing 17q gain (P = 0.0021). This suggests that 17q gain as a prognostic factor plays a more crucial role in low-stage tumours. Expression of the somatostatin receptor 2 (SSTR2), localized in chromosome region 17q24, has in previous studies been shown to be positively related to survival in neuroblastoma. A point mutation in the SSTR2 gene has earlier been reported in a human small-cell lung cancer. In this study, mutation screening of the SSTR2 gene in 43 neuroblastoma tumours was carried out with polymerase chain reaction-based single-stranded conformation polymorphism/heteroduplex (SSCP/HD) and DNA sequencing, and none of the tumours showed any aberrations in the SSTR2 gene. These data suggest that mutations in the SSTR2 gene are uncommon in neuroblastoma tumours and do not correlate with either the 17q gain often seen or the reason some tumours do not express SSTR2 receptors. Overall, this study indicates that gain of chromosome arm 17q is the most frequently occurring genetic alteration, and that it is associated with established prognostic factors.
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| 10. |
- Abrahamsson, Hans, 1966
(författare)
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On Turbulent Wall Jets
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An experimental investigation of the two- and three-dimensional turbulent wall jets has been conducted. The measurements have been performed using different hot-wire techniques in large scale wall jet facilities, and the measurements were focused on the fully-developed region of the flow. The two-dimensional wall jet is found to be self-preserving, and the streamwise development of the maximum mean velocity and the half-width is independent of the inlet Reynolds number when the viscosity and inlet momentum flux are used as scaling parameters. The near wall region is characterised by a short universal mean velocity profile and a high turbulence level caused by the influence of the outer region. The lateral spreading rate of the three-dimensional wall jet is found to be five times larger than the normal spreading rate, and this is connected to a secondary mean motion in the lateral plane which shows a negative normal mean velocity and a sharp twist of the velocity vector away from the symmetry plane near the wall. The turbulent kinetic energy budget indicates a transport of turbulent energy by advection and turbulent diffusion towards the wall region, where the turbulence level is enhanced and the near wall peak in the streamwise turbulence intensity is attenuated. A similarity analysis of the equations governing the 2DWJ show that the shear stress in the outer region scales with the friction velocity instead of the commonly used maximum mean velocity, and thus the outer region is governed by two velocity scales. The similarity analysis also shows that the growth of the wall jet (i.e. the half-width) is not linear but depends on the local Reynolds number. The velocity profiles in the overlap region are not logarithmic (as commonly believed) but show a power law behaviour. The similarity theory is in good agreement with experimental observations. Pulsed hot-wire anemometry measurements (PHWA) show good agreement with LDA data in the outer region of the 2DWJ, and these techniques give a significantly higher turbulence level (e.g. the shear stress) than the HWA. This difference can be explained by the high local turbulence levels, which are so high that local flow reversals occur. Even larger differences between PHWA and HWA are found in the 3DWJ because the local turbulence levels are higher and negative velocity samples are more frequent in the 3DWJ than the 2DWJ.
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