| 1. |
- Lindgren, Göran, 1948-
(författare)
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Studies in conflict economics and economic growth
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- “Armaments and Economic Performance”. The literature on military expenditure (milex) is scrutinized with respect to five areas. Investment is reduced when milex increases. Most studies have found economic growth hindered by higher milex. No clear association between milex and employment is found. However, the same amount of other public expenditure creates more jobs. There is some evidence for milex as counter-cyclical instrument in the US. The result for studies if milex is used in electoral cycles in the US is contradictory. Disaggregated data are emphasized as a possible solution to get more definite results.“The Economic Costs of Civil Wars”. The empirical studies of the economic costs of internal armed conflicts are divided into accounting and modelling methods. Cost is seen as the difference between the counterfactual production without conflict and the actual production. The average economic cost of internal armed conflict is a 3.7% yearly reduction of GDP. There are large differences between the estimates. One of the reasons for pursuing such studies is to give improved basis for more cost-effective post-conflict reconstruction, which is better achieved with an accounting method.“War and Economic Performance – Different Data, Different Conclusions?” This article studies the importance of armed conflict for economic growth by replicating an earlier analysis with new data on conflicts. The basic model investigates how conflicts in 1960-1974 affect economic growth in 1975-1989. Koubi finds that “wars are conducive to higher growth”. Koubi’s finding is confirmed when different conflict data is used in a similar research design.“The Role of External Factors in Economic Growth: A Comparative Analysis of Thailand and the Philippines 1950-1990”. Can differences in economic performance be explained by external factors? Both historical and regression analyses are utilised to answer the question. Three external factors are analysed: International trade, foreign direct investment, and external debt. In the regression analysis none of the external factors qualify as statistically significant. The historical analysis finds two external factors discriminating between the two countries. Thus, they might explain the differing growth rates of Thailand and the Philippines: Manufactured exports and external debt.
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| 2. |
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| 3. |
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| 4. |
- Andersson, Jonas, et al.
(författare)
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Volatility modeling in the presence of measurement errors
- 2001
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Ingår i: Journal of Risk. - 1465-1211. ; 3:4, s. 53-67
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the authors examine the effects of measurement errors on volatility measures. This is done by first expressing the moment properties of general volatility models with measurement errors in terms of the corresponding moments for the underlying unobserved signal process. Then the consequences of measurement errors for some GARCH and stochastic volatility models are evaluated. It is shown that measurement error causes the autocorrelation function, here for the squared process, to start and remain lower than for the underlying unobserved signal process. The size of the effects are highly dependent on the degree of persistence in the volatility. Finally, the consequences of measurement errors on time-varying VaR measures are studied.
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| 5. |
- Eriksson, Olle, et al.
(författare)
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Mood changes correlate to changes in brain serotonin precursor trapping in women with premenstrual dysphoria.
- 2006
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Ingår i: Psychiatry research. - : Elsevier BV. - 0165-1781 .- 0925-4927 .- 1872-7506. ; 146:2, s. 107-16
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Tidskriftsartikel (refereegranskat)abstract
- The cardinal mood symptoms of premenstrual dysphoria can be effectively treated by serotonin-augmenting drugs. The aim of the study was to test the serotonin hypothesis of this disorder, i.e. of an association between premenstrual decline in brain serotonin function and concomitant worsening of self-rated cardinal mood symptoms. Positron emission tomography was used to assess changes in brain trapping of 11C-labeled 5-hydroxytryptophan, the immediate precursor of serotonin, in the follicular and premenstrual phases of the menstrual cycle in eight women with premenstrual dysphoria. Changes in mood and physical symptoms were assessed from daily visual analog scale ratings. Worsening of cardinal mood symptoms showed significant inverse associations with changes in brain serotonin precursor trapping; for the symptom "irritable", r(s)=-0.83, and for "depressed mood" r(s)=-0.81. Positive mood variables showed positive associations, whereas physical symptoms generally displayed weak or no associations. The data indicate strong inverse associations between worsening of cardinal symptoms of premenstrual dysphoria and brain serotonin precursor (11C-labeled 5-hydroxytryptophan) trapping. The results may in part support a role for serotonin in premenstrual dysphoria and may provide a clue to the effectiveness of serotonin-augmenting drugs in this disorder but should, due to small sample size and methodological shortcomings, be considered preliminary.
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| 6. |
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| 7. |
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| 8. |
- Garcia, Maria-José
(författare)
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Engineering rubber bushing stiffness formulas including dynamic amplitude dependence
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Engineering design models for the torsion and axial dynamic stiffness of carbon black filled rubber bushings in the frequency domain including amplitude dependence are presented. They are founded on a developed material model which is the result of applying a separable elastic, viscoelastic and friction rubber component model to the material level. Moreover, the rubber model is applied to equivalent strains of the strain states inside the torsion or axial deformed bushing previously obtained by the classical linear theory of elasticity, thus yielding equivalent shear moduli which are inserted into analytical formulas for the stiffness. Therefore, unlike other simplified approaches, this procedure includes the Fletcher-Gent effect inside the bushing due to non-homogeneous strain states. The models are implemented in Matlab®. In addition, an experimental verification is carried out on a commercially available bushing thus confirming the accuracy of these models which become a fast engineering tool to design the most suitable rubber bushing to fulfil user requirements. Finally, they can be easily employed in multi-body and finite element simulations
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| 9. |
- Hagnestål, Anders, et al.
(författare)
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Coil design for the straight field line mirror
- 2009
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Ingår i: Fusion science and technology. - 1536-1055 .- 1943-7641. ; 55:2T, s. 127-130
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Tidskriftsartikel (refereegranskat)abstract
- Coil systems for producing the Straight Field Line Mirror field using axisymmetric and quadrupolar coils are calculated. Two applications are intended, a fusion-fission nuclear waste transmutation device and a small plasma deposition device. Position, size and current for the axisymmetric coils are optimized as well as radial profile and current for the quadrupolar coils for the two applications. Calculations show that such a coil system can produce the Straight Field Line Mirror field for long-thin mirrors with moderate mirror ratio, but some other coil configuration needs to be found for mirrors where the coils cannot reside close to the plasma edge. In this work, the material science experiment mirror can be produced with about 1% error but the fusion-fission device field has not at this moment been reproduced with acceptable errors.
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| 10. |
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| 11. |
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| 12. |
- Johnson, Steven D., et al.
(författare)
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Pollination success in a deceptive orchid is enhanced by co-ocurring rewarding magnet plants
- 2003
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 84:11, s. 2919-2927
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Tidskriftsartikel (refereegranskat)abstract
- It has been debated whether pollination success in nonrewarding plants that flower in association with nectar-producing plants will be diminished by competition for pollinator visits or, alternatively, enhanced through increased local abundance of pollinators (the magnet species effect). We experimentally evaluated these effects using the nonrewarding bumblebee-pollinated orchid Anacamptis morio and associated nectar-producing plants at a site in Sweden. Pollination success (estimated as pollen receipt and pollen removal) in A. morio was significantly greater for individuals translocated to patches of nectar-producing plants (Geum rivale and Allium schoenoprasum) than for individuals placed outside (20 m away) such patches. These results provide support for the existence of a facilitative magnet species effect in the interaction between certain nectar plants and A. morio. To determine the spatial scale of these interactions, we correlated the visitation rate to flowers of A. morio with the density of sympatric nectar plants in 1-m2 and 100-m2 plots centered around groups of translocated plants, and at the level of whole meadows (0.5–2 ha). Visitation rate to flowers of A. morio was not correlated with the 1-m2 patch density of G. rivale and A. schoenoprasum, but showed a significant positive relationship with density of these nectar plants in 100-m2 plots. In addition, visitation to flowers of A. morio was strongly and positively related to the density of A. schoenoprasum at the level of the meadow. Choice experiments showed that bees foraging on the purple flowers of A. schoenoprasum (a particularly effective magnet species) visit the purple flowers of A. morio more readily (47.6% of choices) than bees foraging on the yellow flowers of Lotus corniculatus (17% of choices). Overall similarity in flower color and shape may increase the probability that a pollinator will temporarily shift from a nectar-producing “magnet” plant to a nonrewarding plant. We discuss the possibility of a mimicry continuum between those orchids that exploit instinctive food-seeking behavior of pollinators and those that show an adaptive resemblance to nectar-producing plants.
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| 13. |
- Johnsson, Roger, et al.
(författare)
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Cylinder pressure reconstruction from vibration and speed measurements on IC engines
- 2004
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Ingår i: Noise and vibration engineering. - Heverlee : Katholieke Univ. Leuven. - 9073802822 ; , s. 965-974
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Konferensbidrag (refereegranskat)abstract
- Knowledge of the in-cylinder pressure pulse in IC engines is of main importance in order to fulfill the requirements on low fuel consumption, exhaust emissions and noise. Direct measurements of the in-cylinder pressure are not suitable outside the laboratory environment due to a number of drawbacks. In this paper a combined indirect method for the measurement of the cylinder pressure pulse is developed and verified. The method is based on linear transfer functions between cylinder pressure and engine vibration and crankshaft speed, respectively. The combined method shows better results than achieved by either method separately. The low frequency part of the pressure pulse is reconstructed from crankshaft speed measurements while the high frequency part is reconstructed from vibration measurements. However, there is still a frequency region between the methods where neither method gives a reliable prediction.
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| 14. |
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| 15. |
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| 16. |
- Johnsson, Roger, et al.
(författare)
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Prediction of points and tendencies of the pressure waveform from crankshaft speed measurements
- 2000
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Ingår i: Proceedings of ISMA 25, 2000 International Conference on Noise and Vibration Engineering. - Leuven : Katholieke universiteit. - 9073802725 ; , s. 907-12
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Konferensbidrag (refereegranskat)abstract
- Direct measurements of the pressure inside the engine have a number of limitations that makes the method expensive and only good for laboratory measurements. Therefore an indirect method to measure the pressure is of main interest. In this study a method based on the crankshaft angular speed fluctuation using neural network has been developed. Two points on the pressure pulse have been reconstructed maximum pressure (Pmax) and start of combustion (SOC). Pmax is predicted with an accuracy of 7.7 MPa and SOC with an accuracy of 1.3 degrees.
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| 17. |
- Jonsson Čabrajić, Anna V, 1978-
(författare)
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Modeling lichen performance in relation to climate : scaling from thalli to landscapes
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lichens can colonize nearly all terrestrial habitats on earth and are functionally important in many ecosystems. Being poikilohydric, their active growth periods are restricted to periods when the thallus is hydrated from atmospheric water sources, such as rain, fog and high relative humidity. Since lichen hydration varies greatly over time lichen growth is therefore more difficult to model compared with, for example vascular plants with more even water supply. I developed two models to predict lichen hydration under field conditions that incorporates the atmospheric water potential (Ψair), derived from air temperature and humidity, only or in combination with species-specific rehydration and desiccation rates. Using Ψair allows the prediction of hydration induced by several water sources. These models were very accurate for epiphytic lichens with a close coupling to atmospheric conditions, but they were less accurate for mat-forming lichens with substantial aerodynamic boundary layers. The hydration model was further developed to include photosynthetic activation for different species, in order to compare their performance under different micro-climatic scenarios. Water balance and activation rate had large effects on lichen activity and were positively related to habitats providing long hydration periods, for example close to streams. To study effects of climate change, a complete model for net carbon gain (photosynthesis minus respiratory losses) was developed for an epiphytic lichen with intricate responses to light, hydration and temperature. Simulation responses in different climate scenarios revealed that projected climate change on a regional scale resulted in varied local scale responses. At the lighter, exposed sites of a forest, the growth responses were positive, but were potentially negative at darker sites with closed canopy. At the local scale, fluctuating hydration, summed irradiance when wet and Chlorophyll a are variables that predict lichen growth. However, at a landscape scale, these variables may be too detailed. We tested this for two terrestrial, mat-forming lichens and developed statistical models for lichen growth in the widest possible climatic gradient in northern Scandinavia, varying in light, temperature and precipitation. Light was the most important factor for high growth at the landscape scale, reaching saturation at a site openness of 40 %, equivalent to a basal tree area of 15 m2 ha -1 in this study. Thereafter, hydration was the next limiting factor, which could be well described by precipitation for one of the species. The simplest predictor was the normal temperature in July, which was negatively correlated with growth. It was apparent that the predictive variables and their power varied at different scales. However, light and hydration are limiting at all scales, particularly by light conditions when lichens are wet. This implies that ensuring that there is sufficient light below the forest canopy is crucial for lichen growth, especially for mat-forming lichens. Hydrophilic lichens may be better preserved in open habitats with long hydration periods. It was shown that models can be powerful and “easy to use” tools to predict lichen responses in various habitats and under different climate scenarios. Models can therefore help to identify suitable habitats with optimal growth conditions, which is very important for the conservation and management of lichens and their habitats.
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| 18. |
- Larsson, Magnus, 1977-
(författare)
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To Bee or Not to Be : Critical Floral Resources of Wild-Bees
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent decades, the development of strategies to prevent or slow the loss of biodiversity has become an important task for ecologists. In most terrestrial ecosystems wild-bees play a key role as pollinators of herbs, shrubs and trees. The scope of this thesis was to study 1) pollinator effectiveness of specialist bees vs. generalist flower-visitors, 2) critical floral resources for wild-bees, and 3) methods to estimate the size of wild-bee populations. The wild-bee species Andrena hattorfiana and A. marginata were used as model species. These two species are specialized on pollen from the plant family Dipsacaceae.The bee A. hattorfiana was found to be a frequent visitor but a poor pollinator of its preferred food-plant Knautia arvensis. The female bees exert such a strong preference for pollen-producing inflorescences that they likely have deleterious effects on the plant, harvesting valuable pollen that could have been transferred to conspecific stigmas by other flower-visitors. To explore the relationship between wild-bees and their food-plants, the concept of pollen budget was developed. We quantified pollen production in the food-plant population and pollen consumption of wild-bee nests. A survey of the visitation by all flower-visitor taxa indicated that the degree of utilization (the fraction of the total pollen amount that is harvested and utilized by A. hattorfiana) varied from 12% to 80% among K. arvensis populations (N=26). The bee Andrena marginata utilized 44% of the pollen production in a population of Succisa pratensis. The pollen budget suggests that with an average flower-visitor diversity and abundance, 330 individuals of the food-plant K. arvensis are required to sustain a population of 20 A. hattorfiana ♀ (the approximate median natural population size). Based on a study of A. hattorfiana, considerable simplifications were proposed for the commonly used mark-recapture design for measuring wild-bee population size. For this species, population size estimated based on mark-recapture data was strongly correlated with the number of observations per survey-walk. The results suggest that large-scale surveys of solitary bee species can be simplified by performing survey-walks.The pollen budget and the method proposed for estimating the size of bee populations have the potential to become valuable tools for monitoring and management of wild-bee populations.
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| 19. |
- Lenfeldt, Niklas, et al.
(författare)
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Cerebrospinal fluid pulse pressure method: a possible substitute for the examination of B waves
- 2004
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Ingår i: Journal of Neurosurgery. - : American Association of Neurological Surgeons. - 0022-3085 .- 1933-0693. ; 101:6, s. 944-950
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Tidskriftsartikel (refereegranskat)abstract
- Object. The appearance of numerous B waves during intracranial pressure (ICP) registration in patients with idiopathic adult hydrocephalus syndrome (IAHS) is considered to predict good outcome after shunt surgery. The aim of this study was to describe which physical parameters of the cerebrospinal fluid (CSF) system B-waves reflect and to find a method that could replace long-term B-wave analysis.Methods. Ten patients with IAHS were subjected to long-term registration of ICP and a lumbar constant-pressure infusion test. The B-wave presence, CSF outflow resistance (Rout), and relative pulse pressure coefficient (RPPC) were assessed using computerized analysis. The RPPC was introduced as a parameter reflecting the joint effect of elastance and pulsatory volume changes on ICP and was determined by relating ICP pulse amplitudes to mean ICP.Conclusions. The B-wave presence on ICP registration correlates strongly with RPPC (r = 0.91, p < 0.001, 10 patients) but not with CSF Rout. This correlation indicates that B waves—like RPPC—primarily reflect the ability of the CSF system to reallocate and store liquid rather than absorb it. The RPPC-assessing lumbar short-term CSF pulse pressure method could replace the intracranial long-term B-wave analysis.
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| 20. |
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| 21. |
- Ljunggren, Fredrik, et al.
(författare)
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Development of a new damper to reduce resonant vibrations in lightweight steel joist floors
- 2002
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 63:11, s. 1267-1280
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Tidskriftsartikel (refereegranskat)abstract
- Floor vibrations annoying to humans often occur in lightweight constructions. A number of methods to solve the problem of resonant vibrations are reported in the literature. Tuned mass damper, semi-active tuned vibration absorber and active control system are all examples of existing methods. A new method has been tested in laboratory environment on a prefabricated floor containing a resilient ceiling with a size up to 6.8×4.8 m2. The method takes advantage of small pieces of visco-elastic material connected between the ceiling joists and the primary beams. A finite element model is used to calculate the correct amount of visco-elastic material. The new damper is especially effective in damping mode shapes where the ceiling oscillates out of phase relative to the floor but shows improvements for other mode shapes as well.
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| 22. |
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| 23. |
- Ljunggren, Fredrik, et al.
(författare)
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Dynamic and subjective analysis of a lightweight/semi-heavyweight floor in a laboratory
- 2006
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Ingår i: Building Acoustics. - : SAGE Publications. - 1351-010X .- 2059-8025. ; 13:4, s. 255-272
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Tidskriftsartikel (refereegranskat)abstract
- A lightweight steel framed floor was tested in a laboratory for eight configurations: continuous/lumped main support, support/unsupported free long sides and concrete/plasterboard as top. The dynamic properties were revealed by modal analysis and subjective evaluations in terms of body perception and perception of vibrating articles. The results showed that the tested parameter that affects the floor most was the top layer. The semi-heavy weight floor with concrete layer was in general judged to be of higher acceptance than the lightweight floor having plaster-boards on the top. Additionally, the lightweight floor was used in a series of experiments where the effect of modified support and the effect of adding line loads of various degree of mechanical connection were tested. This part aims to simulate how the dynamics of a floor stepwise might change going from a bare floor to a floor installed inside a real building. The results show that the line load, mass and stiffness influence the floor in terms of changed natural frequencies. Depending on where on the floor the loads are located, different modes were affected and, depending on how the loads were connected to the floor, the gained stiffness varied slightly
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| 24. |
- Ljunggren, Fredrik, et al.
(författare)
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How to improve impact sound insulation in a lightweight module based building system
- 2007
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Konferensbidrag (refereegranskat)abstract
- This paper covers the initial work in a project where the focus is to improve impact sound insulation for a lightweight module based building system. The size of each module could typically be a small apartment (one room student apartment) or a part of a larger apartment (like two bedrooms or a living room). Modules are prefabricated in a factory, indoors, and are then assembled together at the building yard to form a complete multi-storey building up to fives floors.This building technique often suffers from poor impact sound insulation, especially at low frequencies. A number of parameters that potentially affect the impact sound have undergone experimental testing performed on a setup of two modules, one upper and one lower. Examples of tested parameters: single vs. double layer of floor plaster boards, grey rag boards vs. underlayer foam under the parquet flooring, varying load (weight) on the module and varying kind of vibration insulation in between the modules.
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| 25. |
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| 26. |
- Ljunggren, Fredrik, et al.
(författare)
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Human vibration perception from single- and dual-frequency components
- 2007
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 300:1-2, s. 13-24
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Tidskriftsartikel (refereegranskat)abstract
- This paper covers three different studies with respect to human perception of vertical vibrations. Although the amplitudes and frequencies throughout the experiments are set to match those that might occur in lightweight floor constructions, the results can be seen as general. A motion simulator generates signals from 5 to 31.5 Hz and the test subjects receive the vibrations sitting on a wooden chair. In the first study, the absolute threshold values from sinusoidal signals are determined. The results agree reasonably well with those found from other similar studies. In study number two, threshold values are determined in the presence of an 8 Hz base component. The threshold values were generally found to be higher than those obtained in the first study, except in the case of 10 Hz which due to beating effect gave an even lower threshold level than when the signal was played alone. The third study is about annoyance from dual sinusoidal vibrations, always including a base signal of 8 Hz at fixed amplitude. In similarity with study two, test persons reported to be more annoyed as the second signal component gets close to the base frequency and, naturally, they also got more annoyed as the amplitude increased.
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| 27. |
- Ljunggren, Fredrik, et al.
(författare)
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Minor construction measures that influence vibrations in lightweight floors
- 2003
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Ingår i: Proceedings of the 10th International Congress on Sound and Vibration (ICSV10). - : Institute of Acoustics. ; , s. 4579-4586
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Konferensbidrag (refereegranskat)abstract
- The minor construction measures that influence vibration in lightweight floors were presented. A lightweight steel framed floor equipped with a resilient ceiling was used as test object under laboratory conditions. The ceiling joist stiffness was analyzed by a finite element model where both thickness of material and position of the mounting screws were considered. Two different kinds of joists were tested on a floor section. The effect of a visco-elastic material in conjunction with the joists, to increase the damping, were also shown.
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| 28. |
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| 29. |
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| 30. |
- Mosharrof, Mohammad Sazzad, et al.
(författare)
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Prediction model for the impact sound pressure level of decoupled lightweight floors
- 2009
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Ingår i: 38th International Congress and Exposition on Noise Control Engineering 2009. - Red Hook, NY : Curran Associates, Inc.. - 9781615676903 ; , s. 2038-2046
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Konferensbidrag (refereegranskat)abstract
- Prediction of impact sound insulation in timber buildings is difficult since the constructions are complex, non isotropic and show large variances. There are earlier publications on precise models of simplified structures and simplified models of complex structures, where so far, none is considered as an acceptable simplified engineering model tool. The goal of our research is to develop methodology for such a simplified engineering tool. The starting focus is to model impact sound in a simple floor model of two plates that are realistically coupled via beams. The floor structure in Nordic countries is mostly decoupled, meaning there is either no structural connection or an elastic connection between the plates and the beams. In this paper, an improved floor model is proposed where as a first step there is no physical connection between the plates and beams, and where each plate is stiffened by separate beams. Hence the construction becomes more realistic as only coupling between the plates via air trapped inside the cavity is taken into account. Next step will be to introduce resilient coupling between the respective beams. The modelling show promising results with reasonable sound insulation improvements.
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| 31. |
- Nybacka, Mikael, et al.
(författare)
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Project: CASTT - Centre for Automotive Systems Technologies and Testing
- 2007
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Annan publikation (populärvet., debatt m.m.)abstract
- Through the Centre for Automotive Systems Technologies and Testing, Luleå University of Technology aims to first of all support automotive winter testing in Northern Sweden. This means to support the local automotive test entrepreneurs and through them their customers: the car manufacturers and their suppliers. To succeed in this task, the center relies on the university's areas of leading research and most importantly on the cooperation between those areas.
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| 32. |
- Odelius, Johan, et al.
(författare)
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Communication quality for students with hearing impairment : a study evaluating speech intelligibility and annoyance
- 2005
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Ingår i: Proceedings Forum Acusticum. - : Scientific society for optics, acoustics, motion picture and theater technology. ; , s. 2709-2714
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Konferensbidrag (refereegranskat)abstract
- New pedagogical views on assistive listening devices have enlightened the technology's impact on communication patterns among students with a hearing impairment. The objective of this study was to find methods to evaluate assistive listening devices supporting a more dialogue-oriented and participatory learning environment. With this approach a three-dimensional communication quality definition was proposed. The dimensions are: 1) Speech intelligibility 2) Ambient sounds; annoyance and feeling of presence 3) Parameters concerning the students' performance given the aim and task of the pedagogical situation. In this experiment dimensions 1 and 2 were evaluated, where dimension 2 concerned annoyance. Speech intelligibility was assessed using just-follow-conversation (JFC) tasks performed by normal hearing subjects. The task consisted of adjusting the level of a masker until the listener felt he or she just could understand what was being said. In conjunction with the JFC task, the subjects were asked to estimate the annoyance of the masking signal on an eleven-point scale. The speech and masking signals were filtered by impulse responses generated in a room acoustic model. Design variables were: A) Room acoustic model; two acoustic properties B) Distance between speech source and microphone; 0.75 m or 1.5 m C) Noise masker; speech-spectrum random noise or structure-borne noise D) Microphone directivity; omni-directional or delay-and-sum beamformer E) Amplifier; linear or compression.
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| 33. |
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| 34. |
- Olsson, Per-Anders, 1971, et al.
(författare)
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Effects on gravity from non-tidal sea level variations in the Baltic Sea
- 2009
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Ingår i: Journal of Geodynamics. - : Elsevier BV. - 0264-3707. ; 48:3-5, s. 151-156
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Tidskriftsartikel (refereegranskat)abstract
- The main purpose of this paper is to investigate numerically the effects of non-tidal sea level variations in the Baltic Sea on gravity with special emphasis on the Swedish stations in the Nordic Absolute Gravity Project.To calculate the ocean loading effect on gravity the method described by Farrell (1972) is widely used. This method is based on convolution of a Green's function for gravity with the ocean load, but does not include the direct attraction depending on the height of the observation point. It is described how this effect is included in the Green's functions and how numerical integration is performed over a dense grid bounded by a very high resolution coastline. The importance of this high resolution is shown. The major part of the direct attraction for stations close to the coast comes from relatively small water masses close to the station. The total effect from the Baltic Sea, crustal loading and direct attraction, is calculated for 12 Swedish and one Finnish absolute gravity stations. The distance from the coast for these stations varies from 10 m to 150 km. It is shown that the total non-tidal gravity effect is significant, easily reaching values of 2–3 μgal for stations with high elevation close to the coast.In modelling the Glacial Isostatic Adjustment (GIA), the relation between the change of gravity and the absolute land uplift ((dg/dt) / (dh/dt)) contains information about the viscoelastic properties of the upper mantle. The Baltic Sea is located in the Fennoscandian postglacial land uplift area and experiences therefore a long-term sea level decrease. It is also shown that the magnitude of this long-term effect is not negligible for determination of the unknown part of (dg/dt) / (dh/dt).
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| 35. |
- Petersson, Anders, et al.
(författare)
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Constitutive behaviour of WC-Co materials with different grain size sintered under load
- 2004
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 52:7, s. 1847-1858
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Tidskriftsartikel (refereegranskat)abstract
- The deformation during sintering under an applied uniaxial load was investigated experimentally for two WC-Co cemented carbides with different grain size. The lower applied loads changed only the relative magnitude of axial and radial shrinkages, whereas the higher loads also affected the volumetric strain. Local maxima in shrinkage rate were found at relative densities close to 0.8 for all sintering conditions. The constitutive parameters uniaxial viscosity, Poisson's ratio and sintering stress were empirically modelled as functions of temperature and relative density.
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| 36. |
- Petersson, Anders, et al.
(författare)
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Modelling WC-Co sintering shrinkage - Effect of carbide grain size and cobalt content
- 2007
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 452, s. 37-45
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Tidskriftsartikel (refereegranskat)abstract
- Phenomenological models based on the constitutive parameters uniaxial viscosity, viscous equivalent of Poisson's ratio and sintering stress are used to describe WC-Co sintering shrinkage. Shrinkage is divided into three subsequent stages. The influences of carbide grain size and cobalt content are accounted for and model parameters numerically adjusted to dilatometer results. The model successfully represents published shrinkage data for different materials and milling procedures.
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| 37. |
- Romild, Ulla, 1959-
(författare)
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Essays on Distance Based (Non-Euclidean) Tests for Spatial Clustering in Inhomogeneous Populations : Adjusting for the Inhomogeneity through the Distance Used
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consits of four papers dealing with distance based (non-Euclidean) tests for spatial clustering in inhomogeneous populations. The density adjusted distance (DAD), which considers the underlying density, is defined in the first paper. The proposed distance can be used together with any of the old distance based methods developed for traditional homogeneous spatial patterns. The test statistics in distance based tests can all be seen as a weighted sum of distance measures for distances between n cases with known co-ordinates. DAD based test statistics are developed and their performance is compared with the performance of previously suggested tests by simulation in the second paper. The tests are compared in different types of data set and for various kinds of clustering. It is shown that no test is the optimal choice for all alternative hypotheses and that the tests are unequally sensitive to the structure of the underlying data. Tests based on the DAD are often a good alternative. Test statistics and graphical tools for the Empirical Distribution Function of DAD are developed and examined in the third paper. We show that the result of an EDF test combined with EDF plots provides more information about the possible nature of clustering in a sample than the result of a parametric test only.
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| 38. |
- Rubensson, Emanuel, 1979-
(författare)
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Sparse Matrices in Self-Consistent Field Methods
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is part of an effort to enable large-scale Hartree-Fock/Kohn-Sham (HF/KS) calculations. The objective is to model molecules and materials containing thousands of atoms at the quantum mechanical level. HF/KS calculations are usually performed with the Self-Consistent Field (SCF) method. This method involves two computationally intensive steps. These steps are the construction of the Fock/Kohn-Sham potential matrix from a given electron density and the subsequent update of the electron density usually represented by the so-called density matrix. In this thesis the focus lies on the representation of potentials and electron density and on the density matrix construction step in the SCF method. Traditionally a diagonalization has been used for the construction of the density matrix. This diagonalization method is, however, not appropriate for large systems since the time complexity for this operation is σ(n3). Three types of alternative methods are described in this thesis; energy minimization, Chebyshev expansion, and density matrix purification. The efficiency of these methods relies on fast matrix-matrix multiplication. Since the occurring matrices become sparse when the separation between atoms exceeds some value, the matrix-matrix multiplication can be performed with complexity σ(n).A hierarchic sparse matrix data structure is proposed for the storage and manipulation of matrices. This data structure allows for easy development and implementation of algebraic matrix operations, particularly needed for the density matrix construction, but also for other parts of the SCF calculation. The thesis addresses also truncation of small elements to enforce sparsity, permutation and blocking of matrices, and furthermore calculation of the HOMO-LUMO gap and a few surrounding eigenpairs when density matrix purification is used instead of the traditional diagonalization method.
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| 39. |
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| 40. |
- Shi, Wangqing, et al.
(författare)
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Modelling of impact sound insulation of lightweight steel framing floors
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- It is valuable for the house designer to be aware of a structure's acoustic performance from its material properties at the design stage. A simplified calculation procedure is necessary for this purpose. This report concerns the application of a homogeneous plate prediction model in determining the impact sound insulation for the lightweight steel framing floors. The method is a further development of a prediction method for timber floors. In order to calculate driving point impedance of the lightweight steel framing floor, an equivalent method is used in this study to obtain the parameters of the composite lightweight steel framing floor, e.g. floor height, material density and elasticity to replace a composite floor with a homogeneous single plate. The main advantages of this method will be its simplicity and improve the understanding of the impact sound insulation of the lightweight steel framing floors. This method can also give brief information about the acoustic performance of the structure at an earlier design stage.
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| 41. |
- Shi, Wanqing, et al.
(författare)
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Sound insulation and vibration tests for lightweight steel framing floors
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- An experimental study of sound insulation and vibrations of lightweight steel framing floors due to different floor construction set up were performed. Floors with 3m, 5m and 7.2m span were tested. The impact and airborne sound insulation for 3m span floor were measured based on ISO 140 in lab condition. Vibration tests were carried out on all three different spans. The vibration transmission loss of the structure was determined from the surface vibration measurements. The fundamental natural frequency and damping of the structure was obtained from the mobility measurements. The results of the experiments from sound insulation tests for 3m span lightweight steel framing floor show that this type of floor has very good acoustic performance. The comparison of the measurements of the vibration transmission loss from 3m, 5m and 7.2m show that the floors also have good vibration reductions in longer spans.
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| 42. |
- Tingvall, Bror, et al.
(författare)
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Vehicle test system : a pilot study
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vehicle test system and exhaust multi gas equipment for transient measurements in cold climate. A pilot study to demonstrate regional competence of advanced measurement technology for vehicle test companies in north of Sweden.
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| 43. |
- Tingvall, Bror, et al.
(författare)
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Ytterväggars ljudisolering
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Projektets mål är att ta fram mer underlag för en databas för ljudisoleringen på ett antal vanligt förekommande ytterväggskonstruktioner samt olika förbättringsåtgärder av konstruktionerna. Databasen ska sedan kunna användas vid byggteknisk projektering av ytterväggar. Mätresultaten bör lämpa sig att användas som indata till exempelvis standarden EN 12354 och beräkningsprogrammet Bastian eller andra byggberäkningsprogram. Ljudisoleringen på flertal ytterväggskonstruktioner med olika förbättringsåtgärder har testats, företrädesvis "lätta" ytterväggskonstruktioner. En sandwich betongvägg har också ingått i proven. I flera av testerna uppnås stora förbättringar av ljudisoleringen.
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| 44. |
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| 45. |
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| 46. |
- Wennergren, Ann-Christine, 1957-
(författare)
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Dialogkompetens i skolans vardag : En aktionsforskningsstudie i hörselklassmiljö
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In classes for hard-of-hearing pupils there are children and young people with different degrees of impaired hearing, all of whom need hearing aids and technical equipment inthe environment. The initial problem area of the present thesis concerned the pattern of communication in the classroom. Previous research has shown that such communication is strongly affected by the chosen technical solution. The research questions developed successively from the assumption that it is only the teachers that can change the learning environment. In order to achieve a combination of scientific results and improvement,this study has an action research study approach. The overall aim was to illuminate and describe dialogues between different actors in a national school improvement project. Actors in the context were teachers, their pupils and the researcher. The thesis is based on improvement work in which the researcher cooperated with fifty teachers from five schools located in different parts of Sweden. This work involved parallel processes of change, for the pupils in the classrooms and for the participating teachers. The thesis comprises three substudies, two of which are focused on the teachers’ dialogues and one on the pupils’ listening environments. In the last-mentioned substudy, 165 pupils were asked to draw and describe their best listening environment at school. The result showed that the listening role required different environmental conditions, such as a cleaned upsound environment, visual support, conversation rules and comfortable surroundings. A central conclusion was that pupils need to be offered opportunities to verbalise their individual needs in the school environment. The result further showed that the teachers worked in different ways to improve the learning environment and that they introduced structures to support the dialogue between pupils. This happened at the same time as the teachers were trying out tools for their own learning in order to take part in dialogues with colleagues based on confirmations and challenges. Tools used in the learning processes were a logbook, shadowing, facilitating and a net-based dialogue. The analyses showed explicit differences between using the tools and learning through them in the zone of proximal development. In their improvement processes the teachers depended on critical friends in order to be challenged as knowledge developers. Difficulties in giving a balanced response were evident from the net-based forum in which the teachers reported different attempts at change. The study has drawn on sociocultural perspectives on learning in which dialogue competence have been central to learning in the classroom and in the teachers’ occasional communities of practice. The results indicate that teachers, for their professional improvement, require critical friends in alternative forms of learning processes and that pupils as actors require alternative listening environments.
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| 47. |
- Zurita-Villarroel, Grover, et al.
(författare)
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A new approach to diagnostics of the combustion process in diesel engines using vibration measurements : Part I: Reconstruction of cylinder pressure from vibration measurements
- 2003
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Ingår i: International Journal of Acoustics and Vibration. - : International Institute of Acoustics and Vibration (IIAV). - 1027-5851 .- 2415-1408. ; 8:2, s. 68-76
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Tidskriftsartikel (refereegranskat)abstract
- There is a steadily growing demand for reliable, non-invasive measurement methods which can be used to monitor combustion in diesel engines. An effective, non-invasive method would make it possible for those using diesel engines to economically detect malfunctions during combustion. The main objective of this paper is to show how, through reconstruction, it is possible to generate data on combustion parameters, which can then be used for engine diagnostics. The combustion parameters are the maximum cylinder pressure (pmax, ) and the derivative of the pressure rise (dp/da). The idea is based on reconstruction by using the transfer function, TF, from the combustion chamber to the engine surface and the measured vibration response signal of the engine surface. The analysis is based on a non-linear method called complex cepstrum and signal processing techniques. The TFs were modified to fit slightly different situations such as other cylinders of the same engine; where use can be made of symmetry. A new approach based on a new tailor-made window for reconstruction of the cylinder pressure is also presented. A matrix with engine TFs for varying speed and load was obtained. The matrix can be used as a data bank of TFs for reconstruction of the cylinder pressure at different operating conditions. An extensive analysis of the cycle-to-cycle variations was carried out, both for the measured and reconstructed cylinder pressure. The main parameters of the cylinder pressure; the maximum cylinder pressure (pmax, ) and the derivative of the pressure rise (dp/da), are thoroughly examined in order to validate the procedure.
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| 48. |
- Zurita-Villarroel, G., et al.
(författare)
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Reconstruction of cylinder pressure through multivariate data analysis : for prediction of noise and exhaust emissions
- 2004
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Ingår i: Noise Control Engineering Journal. - : Institute of Noise Control Engineering (INCE). - 0736-2501 .- 2168-8710. ; 52:4, s. 154-163
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Tidskriftsartikel (refereegranskat)abstract
- A new approach for reconstructing diesel engine cylinder pressure is presented. The technique is based on vibration measurements on the engine surface with subsequent reconstruction of the cylinder pressure by direct use of multivariate data analysis (MVDA). In order to investigate and evaluate the usefulness of the proposed technique, data from earlier experiments with four in-line, six cylinder, heavy-duty diesel engines have been used. One of the engines, running on ethanol, was tested according to a three factorial central composite face at different speeds and loads, as well as different blends of ethanol/ignition improver. The other engines, running on ordinary diesel, were tested with various loads and speeds. All of the measurements, i.e. cylinder pressure, sound pressure levels, vibration, and exhaust emissions, were performed simultaneously. The results demonstrated that MVDA models could accurately reconstruct cylinder pressures for all six cylinders in a diesel/ethanol engine. The differences between predicted and observed maximum cylinder pressure for 800 rpm were just 0-5%. The investigations also showed the potential of the method to estimate noise emissions and emission of NO x from the ethanol engine; a single partial least square (PLS) model could be used to predict noise and exhaust emissions at three different loads
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| 49. |
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| 50. |
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