| 1. |
- Edström, Krister, et al.
(author)
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Modelling and Simulation of a Switched Power Converter
- 1996
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Reports (other academic/artistic)abstract
- In our earlier work dealing with switched systems we have focused on the conceptual and formal side of the modelling process. In this paper we go one step further and illustrate the practical generation of simulation code from a switched bond graph. The principles are illustrated by means of an industrial switched power converter used to control the power of electric rotary machines. We describe an implementation of the formal Mode Transition System (MTS) presented earlier. The format proposed is referred to as Mode Transition File (MTF) format. We present an algorithm to generate the mode transition file from a switched bond graph. Finally we illustrate how this file format can be converted to code for the well known DASSRT solver.
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| 2. |
- Grimvall, E, et al.
(author)
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Monitoring of polychlorinated biphenyls in human blood plasma: methodological developments and influence of age, lactation, and fish consumption
- 1997
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In: Archives of Environmental Contamination and Toxicology. - : Springer Science and Business Media LLC. - 0090-4341 .- 1432-0703. ; 32:3, s. 329-336
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Journal article (peer-reviewed)abstract
- Human plasma samples from 50 wives of fishermen have been analyzed with respect to PCBs. The non-ortho-substituted PCB congeners CB-126 and CB-169 were determined by mass spectrometry in negative ion chemical ionization mode, which demonstrated a limit of detection of 30 fg. The recoveries of the internal standards used for determination of ortho-substituted CBs were approximately 95%. Two methods, one gravimetric and the other based on enzymatic determinations of triglycerides, cholesterol and phospholipids, were compared for the determination of total amount of lipids in the plasma samples; the correlation coefficient was 0.82 and the slope 0.98. For practical reasons, enzymatic determinations are recommended for further use. The total, lipid-adjusted concentrations of PCBs in plasma were influenced by age, total lactation time and consumption of fatty fish from the Baltic Sea.
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| 3. |
- Jakobsson, Kristina, et al.
(author)
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Radiological changes in asbestos cement workers
- 1995
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In: Occupational and Environmental Medicine. - 1470-7926. ; 52:1, s. 20-27
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Journal article (peer-reviewed)abstract
- OBJECTIVE--To explore associations between exposure to asbestos cement dust and radiographic findings in lung parenchyma and pleura. METHODS--Radiographs from 174 blue collar workers and 29 white collar workers from an asbestos cement plant formed one part of the study. Progression of small opacities was further studied in those 124 blue collar workers, for whom two radiographs taken after the end of employment were available. The median readings from five readers who used the full ILO 1980 classification were used. As exposure indices, time since start of employment, duration of employment, cumulative exposure, and average intensity of asbestos exposure were used. The influence of age and smoking was also considered in multiple logistic regression analyses. RESULTS--Small opacities (profusion > or = 1/0) were closely correlated with time related exposure variables, and showed weaker association with intensity based exposure variables. The odds ratio (OR) for small opacities was equal to 2.8 (90% CI 1.2, 6.7) in the > 30 f(fibre)-y/ml group, compared with those in the 0-10 f-y/ml group. Progression of at least two minor ILO categories after the end of employment was seen in 20%. Also, pleural thickening was closely related to time. By contrast, costophrenic angle obliterations were not associated with the time related variables, but closely associated with the intensity of asbestos exposure, and tended to occur during employment. The OR was 4.5 (90% CI 1.3, 15) in the > 2 f/ml group, compared with those in the 0-1 f/ml group. CONCLUSIONS--In these workers, exposed mainly to chrysotile but also to small amounts of amphibole, the risk of radiographically visible parenchymal abnormality was substantially increased and strongly dependent on time related exposure variables. Progression was found long after the end of exposure. The findings on costophrenic angle obliterations, supposed to be sequelae of benign pleural effusions, were consistent with an immediate reaction triggered by intense asbestos exposure.
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| 4. |
- Rylander, Lars, et al.
(author)
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Polychlorinated biphenyls in blood plasma among Swedish female fish consumers in relation to low birth weight
- 1998
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In: American Journal of Epidemiology. - 0002-9262. ; 147:5, s. 493-502
-
Journal article (peer-reviewed)abstract
- The authors examined the hypothesized association between the body burden of polychlorinated biphenyls (PCB) in women and the risk of low birth weight for their infants. In Sweden, a main exposure route for PCBs and other persistent organochlorine compounds is through the consumption of fatty fish from the Baltic Sea (on the Swedish east coast). A previous comparison between a cohort of consumers of large quantities of fish from the Swedish east coast and a reference population, together with a following analysis based on questionnaire data from a case-control study within the east coast cohort, supported the hypothesized association. In 1995, blood samples were collected from the wives and ex-wives of fishermen from the Swedish east coast (n = 192) who had given birth during the period 1973-1991. Cases (n = 57), i.e., infants with low birth weight (1,500-2,750 g), were matched with controls (n = 135; birth weight, 3,250-4,500 g) on gender, parity, and calendar year of birth. The concentration of 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) in plasma was analyzed; it has been suggested that CB-153 is a relevant biomarker of exposure to PCBs. The concentration of CB-153 in the plasma of mothers during the year of childbirth was "estimated" using some alternative plausible kinetic models. For two alternative estimated exposure datasets, which were focused on separately, an increase in the risk of a low birth weight was observed at a CB-153 concentration of 300 and 400 ng/g lipid weight, respectively (adjusted odds ratios of 2.1 (95% confidence interval (CI) 1.0-4.7) and 2.3 (95% CI 0.9-5.9)). The present results strengthen the findings reported previously for this study population.
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| 5. |
- Strömberg, Anna, 1967-, et al.
(author)
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Factors influencing patient compliance with therapeutic regimens in chronic heart failure : A critical incident technique analysis
- 1999
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In: Heart & Lung. - : Elsevier BV. - 0147-9563 .- 1527-3288. ; 28:5, s. 334-341
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Journal article (peer-reviewed)abstract
- Objective: The aim of this study was to identify factors influencing compliance with prescribed treatment in patients with chronic heart failure.Methods: A qualitative design with a critical incident technique was used. Incidents were collected through interviews with 25 patients with heart failure strategically selected from a primary health care clinic, a medical ward, and a specialist clinic.Results: Two hundred sixty critical incidents were identified in the interviews and 2 main areas emerged in the analysis: inward factors and outward factors. The inward factors described how compliance was influenced by the personality of the patient, the disease, and the treatment. The outward factors described how compliance was influenced by social activities, social relationships, and health care professionals.Conclusions: By identifying the inward and outward factors influencing patients with chronic heart failure, health care professionals can assess whether intervention is needed to increase compliance.
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| 6. |
- Strömberg, Jan-Erik, et al.
(author)
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Modelling and Simulation of a Switched Power Converter
- 1997
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In: Proceedings of the Third International Conference on Bond Graph Modeling and Simulation. - 1565551036 ; , s. 195-200
-
Conference paper (peer-reviewed)abstract
- In our earlier work dealing with switched systems we have focused on the conceptual and formal side of the modelling process. In this paper we go one step further and illustrate the practical generation of simulation code from a switched bond graph. The principles are illustrated by means of an industrial switched power converter used to control the power of electric rotary machines. We describe an implementation of the formal Mode Transition System (MTS) presented earlier. The format proposed is referred to as Mode Transition File (MTF) format. We present an algorithm to generate the mode transition file from a switched bond graph. Finally we illustrate how this file format can be converted to code for the well known DASSRT solver.
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| 7. |
- Strömberg, Ulf, et al.
(author)
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Adjustment of a sparse and irregular reference rate matrix
- 1995
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In: American Journal of Epidemiology. - 0002-9262. ; 142:2, s. 212-221
-
Journal article (peer-reviewed)abstract
- Regional sex-specific rates of a rare disease often show conspicuous fluctuations over conventional strata of age and calendar time. In a cohort study, when such rates are used as references in the calculation of the expected number of cases, the accumulated person-time of the study cohort may somewhat haphazardly contribute to the result. For example, only the person-time observed in the strata with at least one reference case registered contnbutes to the expected number of cases. It may therefore be important to evaluate whether the regional rates seem to differ systematically from the more stable national rates. When such differences may be indicated, a fairly simple method is proposed for smoothing rates. This method aims to produce rates that better reflect the underlying, supposedly smooth, rate pattern over age and calendar time in a population of interest. The present paper illustrates the technique by considering right-sided colon cancer incidence rates from a regional male population, which the authors use to calculate the expected number of such cases in an occupational cohort.
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| 8. |
- Söderman, Ulf, et al.
(author)
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Mode Invariant Modelling
- 1995
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Reports (other academic/artistic)abstract
- Modelling of physical systems is a difficult task, in particular if mode switching is allowed. Automated support can be supplied, if two conditions are fulfilled. First, a set of suitable qualitative concepts has to be availiable as a tool box for constructing adequate models. Second, powerful computational machinery must handle model complexity. In this paper we introduce both a conceptual basis and a computational algorithm for dealing with mode switching physical systems. Our approach is more effective than current AIbased methods since it is based on general physical principles at the proper level of abstraction, expressed in terms of bond graphs. The latter formalism is extended in order to deal with mode switching. All meaningful causal modes and transitions between modes are derived automatically. A power electronic circuit serves a guiding example.
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| 9. |
- Söderman, Ulf, et al.
(author)
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Switched Bond Graphs : Multiport Switches, Mathematical Characterization and Systematic Composition of Computational Models
- 1995
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Reports (other academic/artistic)abstract
- Classical bond graphs are in principal restricted to the modelling of continuous physical systems only. In previous work we have extended classical bond graphs to systems involving abrupt changes as well. This extension is centered around the introduction of an ideal primitive switch concept. In this paper we continue this work and extend it in a number of important directions. We present the multiport generalization of the previously introduced primitive one-port switch. We elaborate on the mathematical semantics of individual switch elements as well as complete switched bond graphs, i.e. bond graphs involving one or more switch elements. We discuss the systematic composition of computational models for switched bond graphs and for this purpose we introduce a constructive composition operator. Finally, we also discuss some ideas to deal with model complexity and 'non-physical' modes. Here, the multiport switch plays an important role. For the representation of the composed computation models of switched bond graphs we introduce a mathematical structure related with state automata. This structure is referred to as mode transition systems. For the mathematical characterization of individual switch elements a simplified version of this structure, referred to as switch transition systems, is introduced.
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| 10. |
- Söderman, Ulf, et al.
(author)
-
Switched Bond Graphs : Towards Systematic Composition of Computational Models
- 1995
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In: Proceedings of the 2nd International Conference on Bond Graph Modeling and Simulation. - Linköping : Linköping University. ; , s. 73-79
-
Reports (other academic/artistic)abstract
- In classical bond graph modelling, a computational model is systematically composed from the parts without having to introduce local or global patches. Unfortunately this has not yet been fully carried over to switched bond graphs, i.e. bond graphs employing the ideal switch concept. The focus of this paper is on the systematic composition of the discrete mode transitions. To this end we provide a mathematical structure for the composed computational model and a procedural composition operator. We also outline an algorithm to localize and adjust the composed system in those cases where the composition operator fails. An important concept in this treatment is the generalization of primitive switches to multiport switch fields.
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