| 1. |
- Andersson, Erik, 1962-
(författare)
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A Variational data assimilation scheme and its use of meteorological observations
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Meteorological data assimilation is the process by which a model simulation of the atmosphere is corrected by observations. In operational weather forecasting, this is done in near real-time, to provide accurate initial conditions for numerical forecasts. The accuracy of the forecasts depends crucially on the accuracy of the data assimilation.The increase in available computing power and the theoretical advances in data assimilation methods have recently enabled the European Centre for Medium-Range Weather Forecasts (ECMWF) to develop and introduce operationally a new data assimilation scheme (4D-Var), based on variational methods. The four papers of this thesis present recent developments that have exploited some of the most promising possibilities of 4D-Var with respect to observation usage. They have all been incorporated in operational practice at ECMWF.Variational data assimilation schemes have several advantages that make the new scheme more flexible than earlier schemes with respect to the use of observations. The introduction of 4D-Var has enabled the effective use of a wider range of meteorological observations than previously possible. This includes, as will be demonstrated in this thesis, both conventional observations and satellite measurements.In the first paper we develop a method for the use of satellite radiance observations, and investigate the aspects of 4D-Var that make the scheme particularly well suited for the assimilation of data from a growing variety of space based observing systems. In the second paper we develop a variational quality control method. The third paper investigates the flow-dependence of the 4D-Var response to time series of surface pressure observations in the vicinity of a rapidly developing storm. The final paper presents a diagnostic method for tuning of the 4D-Var system.
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| 2. |
- Bengtsson, Anders, 1954, et al.
(författare)
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Extracorporeal ("ex vivo") connection of pig kidneys to humans. III. Studies of plasma complement activation and complement deposition in the kidney tissue.
- 1998
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Ingår i: Xenotransplantation. - 0908-665X. ; 5:3, s. 176-83
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Tidskriftsartikel (refereegranskat)abstract
- The complement system is one of the important factors involved in the hyperacute rejection of xenografts. This report deals with the activation of the complement system in a clinical trial where pig kidneys were extracorporeally connected to two volunteer dialysis patients who were pretreated with plasmapheresis in order to substantially reduce anti-pig xenoantibodies. The clinical data of the perfusion experiments and the patients humoral immune response to pig xenoantigens have been reported in detail (Xenotransplantation 1996; 3:328-339, 340-353). Three consecutive daily plasmapheresis treatments of the patients reduced the plasma complement protein (C3, C4, and C5) concentrations to 8-27% of the baseline values. The perfusion of the pig kidney connected to patient 1 was terminated at 65 min due to graft rejection and this patient was not hemodynamically affected by the experiment. The second experiment was terminated at 15 min due to an anaphylactic like reaction of the patient. In patient 1 a slight reduction of plasma C3, C4, and C5 and an increase of C5a and SC5b-9 occurred, while C3a decreased during the perfusion. Patient 2 had an increase of all complement parameters, most prominent for C4d and SC5b-9, which occurred concomitant with the appearance of the anaphylactic like side effects. In general, plasma levels of PMN elastase, IL6 and IL8 increased in both patients during the perfusion. Immunohistochemical investigation of the kidney tissues revealed deposition of human complement factors C1q, C4c, and C3c in a congruent pattern with the vasculature of the kidney in patient 1. In kidney 2 only trace amounts of C1q and C3c were found. Both kidneys were negative for properdin. Therefore, in this experimental set up with extracorporeal connection of pig kidneys to the human circulation the human complement cascade is activated mainly through the classical pathway.
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| 3. |
- Bengtsson Boström, Kristina, et al.
(författare)
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Polymorphism in the angiotensin converting enzyme but not in the angiotensinogen gene is associated with hypertension and type 2 diabetes: the Skaraborg Hypertension and diabetes project
- 1999
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Ingår i: Journal of Hypertension. - 1473-5598. ; 17:11, s. 1569-1575
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To study the association between polymorphisms in the angiotensin converting enzyme (ACE) gene and angiotensinogen (AGT) gene and hypertension and/or type 2 diabetes in a community population. PATIENTS AND METHODS: The insertion (I)/deletion (D) polymorphism of the ACE gene and the M235T polymorphism of the AGT gene were genotyped in 773 nondiabetic individuals with hypertension, 193 normotensive patients with type 2 diabetes, 243 patients with type 2 diabetes and hypertension, and in 820 normotensive control individuals identified in a community-based study. RESULTS: The DD genotype was associated with hypertension in individuals less than 70 years [odds ratio (OR) = 1.54, confidence interval (CI) = 1.09-2.18] and remained so when patients with type 2 diabetes were excluded from the analysis (OR = 1.45, CI = 1.01-2.09). The strongest association was with the combination of type 2 diabetes and hypertension (OR = 2.19, CI = 1.09-4.38). There was no association with type 2 diabetes without hypertension. No association was observed between the M235T variant or the 3'-microsatellite polymorphism of the AGT gene and hypertension. CONCLUSION: The D-allele of the ACE gene ID polymorphism increases susceptibility to hypertension, particularly when associated with type 2 diabetes. No association was observed between the M235T variant or 3'-microsatellite polymorphism of the AGT gene and hypertension.
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| 4. |
- Bengtsson, Daniel, et al.
(författare)
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Zipper performance when mixing ADSL and VDSL in terms of reach and capacity
- 1997
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this contribution we have examined how the maximum reach vary at different bit rates on a VDSL system, when different numbers of ADSL and VDSL systems share the same binder. In this context it is concluded that when using the Zipper duplex scheme, VDSL can coexist with ADSL in the same binder without a significant degradation in reach. Further, it is shown that the Zipper duplex scheme secure that ADSL is not disturbed by NEXT from VDSL The Zipper performance has also been compared with both a TDD proposal and a FDD proposal. The results from this comparison shows that Zipper outperforms FDD and TDD in terms of extended reach at all studied mixes of ADSL and VDSL sharing the same binder. For example with a moderate number (5) of ADSL disturbers, the Zipper reach is 150 meters longer than for TDD, and is 350 meters longer than for FDD when studying the medium range asymmetrical bit rate (26:3.2 Mbps).
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| 5. |
- Bengtsson, Lennart, 1969
(författare)
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Efficient Density-Functional-Based Calculational Methods for Surfaces
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the last decades, computer simulations have become an important tool for the study of elementary surface processes, such as atomic and molecular adsorption, diffusion of ad-atoms and surface recombination. The knowledge gained by such studies can be used to understand and develop technologically important processes such as catalysis and crystal growth. Thanks to the exponentially increasing power of computers and the rapid development of efficient numerical algorithms, it is now possible to solve the equations of density functional theory (DFT) for realistic surfaces. This has opened up the possibility of calculating potential energy surfaces that governs elementary surface processes entirely from first principles. Moreover, DFT calculations allows us to predict chemical and physical properties of surfaces. In the thesis, I discuss how a particular implementation of DFT, the plane-wave pseudopotential method, can be used for calculating properties of "real-world" surface processes. Several applications are discussed: adsorption and recombination of atomic hydrogen on copper surfaces, adsorption of molecular hydrogen on stepped copper surfaces, and the growth of the kappa phase of aluminium oxide on a titanium carbide substrate. A few noteworthy results, which are supported by both experimental and theretical studies, are the following: A hydrogen molecule that is adsorbed on a kink atom at a stepped copper surface is found to rotate in a two-dimensional manner. For instance, this unusual quantum rotor state provides a key ingredient for preferential adsorption of ortho hydrogen at this surface. In the study of growth of aluminium oxide using chemical vapor deposition, the previously unknown atomic structure of the kappa phase is determined, and a we present a simple argument for why growth of the meta-stable kappa phase is favoured on the titanium carbide substrate. I also present details about the numerical algorithms and optimization techniques that I have implemented in the DFT code in order to make efficient use of modern computer architectures and reduce the execution time of large simulations.
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| 6. |
- Breimer, Michael, 1951, et al.
(författare)
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Extracorporeal ("ex vivo") connection of pig kidneys to humans. I. Clinical data and studies of platelet destruction.
- 1996
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Ingår i: Xenotransplantation. - : Wiley. - 0908-665X .- 1399-3089. ; 3:4, s. 328-39
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Tidskriftsartikel (refereegranskat)abstract
- The pioneering experiment by Welsh et al. (Immunological Lett 1991:29:167-170) connecting a pig kidney to the human circulation has been repeated in a modified manner. Two volunteer dialysis patients were pretreated by daily plasmapheresis on days -2,-1, and 0 to remove the naturally occurring anti-pig xenoantibodies. The anti-pig lymphocytotoxic liters were reduced from 1:8 to 1:2 in patient 1 and from 1:8 to 1:1 in patient 2. No steroids or immunosuppressive drugs were administrated before or during the experiments. A sterile pig kidney was extracorporeally ("ex vivo") connected to the patients a/v fistula using an arterial and a venous pump similar to a dialysis. The two experiments gave different results. In the first experiment the perfusion pressure was kept at 100 mmHg for the initial 25 min by reducing the pump speed until the minimum blood flow of 30 ml/min was reached. Thereafter, the pressure rose continuously and the experiment was terminated at 65 min at a perfusion pressure of 200 mmHg. The patient did not feel any discomfort during the perfusion. In the second experiment, a stable blood flow of 200 ml/min was reached at a pressure of 100 mmHg after a few minutes. The perfusion was terminated at 15 min when the patient developed chest and abdominal pain, hypotension, and electrocardiographic signs of myocardial ischemia. The patient recovered quickly. In the first experiment, small volumes of clear urine was produced until the pressure rose above 100 mmHg, which resulted in hematuria. In the second experiment clear urine (4 ml/min) was produced. (51)Chromium clearance values were after 15 min <1 ml/min for kidney 1 and 12 ml/min (8 ml/min/100 g) for kidney 2. A drastic reduction in platelet count (128 to 48 and 64 to 8 × 10(9)/1, respectively) during the passage through the kidney was found in blood samples collected simultaneously before and after the organ. No change in hemoglobin values and leucocyte counts were found. Light- and electron-microscopical analysis of the kidney tissues revealed for kidney 1 focal areas with obliteration of the glomerular and peritubular capillaries by platelets and PMN cells and severe damage of the endothelial cells comparable to a picture of a hyperacute rejection. In kidney 2, all vessels were patent but in the capillaries large amount of membrane fragments were detected by electron microscopy and a discrete damage of the endothelial cells were seen in some segments. No intact platelets were present in the vascular tree. These human experiments support the hypothesis that hyperacute rejection of pig to human xenografts is delayed in time by removal of the preformed anti-pig xenoantibodies. A new finding was a very rapid destruction of platelets occurring in the kidney of patient 2 who had very low liters of xenoantibodies. The humoral immune response is described in detail in an accompanying paper (Rydberg et al., this issue).
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| 7. |
- Bøg-Hansen, Erik, et al.
(författare)
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Risk factor clustering in patients with hypertension and non-insulin-dependent diabetes mellitus. The Skaraborg Hypertension Project
- 1998
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Ingår i: Journal of Internal Medicine. - 1365-2796. ; 243:3, s. 223-232
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To assess the coexistence of hypertension and diabetes, associations with cardiovascular risk factors and the achievement of current treatment goals. DESIGN: A community-based, cross-sectional, observational study. SETTING: Hypertension and diabetes outpatient clinics in primary health care, Skara, Sweden. SUBJECTS: All patients (n = 1116; 488 men, 628 women) who performed an annual follow-up from May 1992 to September 1993. MAIN OUTCOME MEASURES: Hypertension, non-insulin-dependent diabetes mellitus (NIDDM), blood pressure, fasting B-glucose, lipids, HbAlc, body mass index (BMI), waist hip ratio (WHR). RESULTS: Hypertension alone was found in 286 men and 430 women, hypertension and NIDDM combined in 102 men and 102 women, and NIDDM alone in 100 men and 96 women. Taking new cases into account, the proportion of hypertension among NIDDM patients was 57%, and the proportion of NIDDM among hypertensives was 26%. Men and women with both hypertension and NIDDM had a higher systolic blood pressure and women also had a higher diastolic blood pressure (men 168/88 mmHg, women 165/86 mmHg) than those with hypertension alone (men 152/87 mmHg, women 156/82 mmHg) (P < or = 0.001). Cardiovascular risk factors accumulated in patients with both hypertension and NIDDM (triglycerides, BMI and WHR). A diastolic blood pressure < or = 90 mmHg was achieved by 71% men and 84% women with hypertension. HbAlc < 7.5% was attained by 71% men and 70% women with NIDDM. CONCLUSIONS: A considerable coexistence of hypertension and NIDDM was demonstrated. Cardiovascular risk factors clustered in patients with both diseases and their blood pressure was less controlled. These patients thus comprised a clinically defined group at high risk. By current guidelines, control of hypertension and NIDDM seemed appropriate.
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| 8. |
- Hult, Roger, et al.
(författare)
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Segmentation of the Brain in MRI Using Grey Level Morphology and Propagation of Information
- 1999
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Ingår i: Proceedings of SCIA'99. - : Pattern Recognition Society of Denmark, Lyngby. - 8788306429 ; , s. 367-373
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Konferensbidrag (refereegranskat)abstract
- An important step in the analysis of 3D MRI brain images is to segment the cortex from surrounding tissue. In this paper we present an algorithm for fully automatic segmentation of the cortex from T1-weighted MRI data. The automatic segmentation starts wi
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| 9. |
- Lundqvist, Roger, et al.
(författare)
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Classification of Functional Patterns in SPECT Brain Scans Based on Partial Least Squares Analysis
- 1999
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Ingår i: Proceedings of SCIA'99. - : Pattern Recognition Society of Denmark, Lyngby. - 8788306429 ; , s. 375-381
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Konferensbidrag (refereegranskat)abstract
- The main purpose of this paper is to show the potential of the partial least squares (PLS) method for finding image descriptors which can be used for classification of clinical single photon emission computed tomography SPECT neuroimaging data. In this ar
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| 10. |
- Thurfjell, Lennart, et al.
(författare)
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A Boundary Approach for Fast Neighborhood Operations on Three-Dimensional Binary Data
- 1995
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Ingår i: Graphical Models and Image Processing. - : ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS. - 1077-3169 .- 1090-2481. ; 57:1, s. 13-19
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents algorithms for fast erosion, dilation, and connected component labeling of three-dimensional binary data, The algorithms are based on a boundary representation of the data where the only voxels stored are those that belong to an object
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| 11. |
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| 12. |
- Thurfjell, Lennart, et al.
(författare)
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CBA—an atlas-based software tool used to facilitate the interpretation of neuroimaging data
- 1995
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Ingår i: Computer Methods and Programs in Biomedicine. - : ELSEVIER SCI PUBL IRELAND LTD. - 0169-2607 .- 1872-7565. ; 47:1, s. 51-71
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Tidskriftsartikel (refereegranskat)abstract
- CBA, a software tool used to improve quantification and evaluation of neuroimaging data has been developed. It uses a detailed 3-dimensional brain atlas that can be adapted to fit the brain of an individual patient represented by a series of displayed ima
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| 13. |
- Thurfjell, Lennart, et al.
(författare)
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Surface reconstruction from volume data used for creating an adaptable functional brain atlas
- 1995
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Ingår i: IEEE Transactions on Nuclear Science. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9499 .- 1558-1578. ; 42:4, s. 1383-1387
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Tidskriftsartikel (refereegranskat)abstract
- Functions for creating adaptable atlas structures from volume data have now been included in the Karolinska Computerized Brain Atlas (CBA) software system. The main objective is to allow the user to create functional structures based on data from brain ac
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| 14. |
- Wehrmann, Felix, et al.
(författare)
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A 3D Deformable Surface Model to Segment the Brain in MR Images
- 1999
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Ingår i: Proceedings of SCIA'99. - : Pattern Recognition Society of Denmark, Lyngby. - 8788306429 ; , s. 289-294
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Konferensbidrag (refereegranskat)abstract
- Our objective was to develop a three dimensional segmentation method for medical Magnetic Resonance images of the brain. The object to be segmented is spatially represented by a deformable surface model with physical-elastic behavior. The special quality
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