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Träfflista för sökning "WFRF:(Lindberg Eva) srt2:(1995-1999)"

Sökning: WFRF:(Lindberg Eva) > (1995-1999)

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1.
  • Broman, Lars, et al. (författare)
  • Enhancing the optical efficiency of a thermophotovoltaic generator using square cones in combination with interference filters
  • 1998
  • Ingår i: Second World Conference on Photovoltaic Solar Energy Conversion. - Wien, Österrike.
  • Konferensbidrag (refereegranskat)abstract
    • The optical efficiency is a week link in all TPV systems. Many different approaches have been studied earlier, but not much on the possibility to use interference filters. Such filters can be designed to get alsmost any desired optical performance, as long as it is allowed to use a large number of layers in the multilayer stack. In practical applications this is very often not acceptable. Nevertheless such filters can still be quite good, at least for a very narrow range of incident angles. Therefore a double-cone geometry is proposed to be used in combination with such filters. This geometry will limit the range of incident angles onto the filter, which will then act more efficiently. The influence of the geometry is evaluated by means of model experiments, and a computer program has been constructed to be able to simulate this type of geometry using ray-tracing technique.
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  • Broman, Lars, et al. (författare)
  • Square cones for TPV: experiments and computer simulations
  • 1998
  • Ingår i: Fourth NREL Conference on Thermophotovoltaic Generation of Electricity. - Denver, CO, USA.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The efficiency of a TPV generator is very dependent on selective optical properties of the chain emitter-filter-TPV cell-reflective backing. If a selective reflective edge filter using multiple reflections in dielectric layers is employed, the slope of the edge depends on the incidence angle interval. A special geometry, consisting of a double square cone between the (square) emitter and the (square) cell array, which narrows this angle interval significantly, has been constructed and investigated experimentally as well as with ray tracing analysis.
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  • Jansson, Anders, et al. (författare)
  • Trafiksäkerhet och informationsmiljö i tågförarsystemet. Litteraturöversikt och olycksfallsanalyser
  • 1999
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • This literature survey focuses on studies of the train driver system and its connections to other parts of the larger train traffic system. The main part of the studies concern Swedish conditions, but other references are included as well.In the first part, different ways of analysing accidents are discussed, including organisational aspects. In the second part, research results from different areas, all assumed to be relevant to the train driver task, are aggregated into a body of knowledge about the train driver system. Comparisons are made between the train driver task and other operator tasks. Further, the effects of a higher degree of automation are discussed.The task of driving a train is modelled as a dynamic decision task, where the driver's mental representation of the technical system and the optic flow of information are assumed to be important parts of the train driver task.In the last part of the literature survey, the content of 40 accident reports is discussed. Further, an analysis and a classification of Swedish train accidents are made by using CREAM (Hollnagel, 1998). The content of the reports, as well as the CREAM-method are evaluated, and different classification criteria are discussed.
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  • Lindberg, Eva (författare)
  • Geometries for enhancing the output from PV cells
  • 1997
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • In a world of limited resources and increasing demand for energy sources, especially in developing countries, PV cells are of great interest. Despite fairly large efforts in certain countries, among them Sweden, in R&D of new technology, the cells are still expensive regarding cost per watt. Obviously there should be interest also in other solutions than increasing cell efficiency for enhancing the output from the PV systems. Some solutions could be different geometries of both the PV cells and the PV cells combined with concentrating equipment such as cones and cornets, lenses, or V-trough mirror concentrators. Geometries studied in this thesis are: square comets, linear Fresnel lenses, V-trough/Fresnel lens combinations, concave and convex cylindrical surfaces, and PV panels mounted an an adjustable rack. Square cornets with flat mirrors have even light distribution at the exit aperture, which is an advantage over circular cornets and CPC cones which have uneven light distribution and cause hot spots at the exit aperture. Measurements and calculations on silver coated and aluminum coated cornets indicated that arrangements with comets having a PV cell at the exit aperture are technically worthwhile. The concentration depends on the geometry of the comet and the reflector material of the surface. The low cost, compared to PV cells, of polished and coated 0.7 mm aluminum makes it probable that the use of cornet concentrators would reduce the cost per produced kWh. Factors to take into account are the higher labor and material costs for manufacturing modules with cornets. Direct sunlight can be concentrated by lenses. Since large ordinary lenses are too bulky, flat linear or circular Fresnellenses are the only practical lenses for solar energy applications. The Fresnel lens is however less perfect than ordinary lenses since not all incident rays hit facets. The linear Czech Fresnel lens is made of glass and mass-produced in an inexpensive and technically simple method, but the surface is not optically perfect due to a slight sagging of the rolled grooved surface during the hardening of the glass. The ray tracing results have therefore been supplemented with measurements. Both rays incident on the flat surface and on the grooved surface were studied, as well as normal incidence and various combinations of meridional and sagittal angles of incidence. The measurements show that focallength varies from 35 cm to 60 cm for focal band widths about 5 cm, depending on incidence angles and whether the flat or grooved surface faces the sun. This Fresnellens could be combined with a PV panel consisting of solar cells connected in series in one row, which is placed in the focal band. The Czech Fresnellens could also be combined with a V-trough mirror concentrator and with one row of PV cells or one long, thin-film PV cell at the bottom of the trough. A test bench has been constructed, and six different geometries have been studied: For all of these geometries four cases have been studied: troughs without the lens, with the flat surface of the lens and the grooved surface facing the sun, and the lens only with the mirrors covered. The concentration was measured by comparing the short circuit current from a PV cell at the bottom of the trough. The measurements indicated that the acceptance angle is larger when the grooved surface faces the sun than when the flat surface faces the sun, but the concentration is slightly larger when the flat surface faces the sun. For the investigated geometries the light concentration varies from 1.9 to 3.2. The reflection losses from a flat surface are large for high incidence angles. At high latitudes a substantial part of the sunlight hits the surface of a stationary PV panel at high incidence angles. In order to reduce the reflection losses one solution could be to produce thin-film PV panels with concave or convex surfaces. Calculations have been carried out for six different refractive indices of the surface and six different ratios between the depth of the curved surface and the width of the surface. For all these combinations the conditions for both one surface and two surfaces (panes) have been calculated. The results show that for transparent concave panes the overall reflection losses could be reduced by one to two percent units compared to a flat surface. The last idea investigated was the improvement of PV panel output by changing the panel azimuth thrice daily. Calculations were carried out for three different latitudes at locations in the north, the middle and the south of Sweden in order to estimate the most suitable azimuths and tilt angles for the three azimuth changes. The calculations show that the insolation could be increased by 38 %,30 %, and 28 %, respectively, as compared with a stationary panel. Measurements were carried out in Borlänge, the middle location. The voltage and current from two panels, one fixed at the best tilt and one turned thrice daily, were measured every sixth minute and stored using a data logger. For four days in July with normal weather the gain was 30 % compared to the stationary panel, and for seven days in August with sunny weather the gain was 39 %. If a simple and inexpensive adjustable mount could be manufactured, this idea would be very interesting in order to enhance the PV output for a small panel of a few modules to be used, for instance, at a summer cottage.
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  • Lindberg, Eva (författare)
  • Snoring and sleep apnea : A study of evolution and consequences in a male population
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Obstructive sleep apnea syndrome (OSAS) is characterized by snoring, repeated apneas during sleep and excessive daytime sleepiness (EDS). The available data suggest that there is a relationship between OSAS and cardiovascular morbidity and mortality, but the results diverge.In 1984, 3,201 men aged 30-69 answered a questionnaire on snoring, sleep disturbances and somatic diseases. A subsample of the men who reported symptoms related to OSAS were also investigated using whole-night polysomnography in 1985.Of the survivors in 1994, almost 90% participated in this 10-year follow-up and answered an identical questionnaire as well as questions about smoking, alcohol and physical activity. In both 1984 and 1994, the prevalence of snoring increased until age 50-60 and then decreased. At all ages, weight gain was an independent risk factor for developing habitual snoring. In men below age 50 at baseline, persistent smoking and a high BMI in 1984 were also significantly associated with the development of snoring.Among the men aged 30-59 in 1984, those who reported habitual snoring in both 1984 and 1994 ran a significantly increased risk of developing hypertension during the 10-year period (adjusted odds ratio 2.6, 95% CI 1.5-4.5). Among the subjects aged 50-69, no association was found between snoring and hypertension.Mortality data for the 10-year period were collected for the complete sample. Compared with subjects with no snoring or EDS, men with both snoring and EDS experienced a significant increase in overall mortality as well as cardiovascular mortality. However, the relative rates decreased with increasing age and, in men aged 60 and over, no effect on mortality was found. Isolated snoring or EDS did not influence mortality at any age.Of the men studied using polysomnography in 1985, 38 (70% of the survivors) were reinvestigated using polysomnography in 1995. In the group as a whole, a significant progression of the sleep disorder with time was found. Increasing EDS was strongly related to a deterioration in the sleep disorder.In conclusion, age strongly influences the prevalence of snoring in men, but the relationship is not linear. Risk factors for developing snoring differ with age and the cardiovascular health consequences appear to be most hazardous in the case of younger men. Sleepy male snorers are a high-risk group for developing OSAS, regardless of the results of the sleep recordings at baseline.
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