| 1. |
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| 2. |
- Auger, A. -T, et al.
(författare)
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Geomorphology of the Imhotep region on comet 67P/Churyumov-Gerasimenko from OSIRIS observations
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583
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Tidskriftsartikel (refereegranskat)abstract
- Context. Since August 2014, the OSIRIS Narrow Angle Camera (NAC) onboard the Rosetta spacecraft has acquired high spatial resolution images of the nucleus of comet 67P/Churyumov-Gerasimenko, down to the decimeter scale. This paper focuses on the Imhotep region, located on the largest lobe of the nucleus, near the equator. Aims. We map, inventory, and describe the geomorphology of the Imhotep region. We propose and discuss some processes to explain the formation and ongoing evolution of this region. Methods. We used OSIRIS NAC images, gravitational heights and slopes, and digital terrain models to map and measure the morphologies of Imhotep. Results. The Imhotep region presents a wide variety of terrains and morphologies: smooth and rocky terrains, bright areas, linear features, roundish features, and boulders. Gravity processes such as mass wasting and collapse play a significant role in the geomorphological evolution of this region. Cometary processes initiate erosion and are responsible for the formation of degassing conduits that are revealed by elevated roundish features on the surface. We also propose a scenario for the formation and evolution of the Imhotep region; this implies the presence of large primordial voids inside the nucleus, resulting from its formation process.
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| 3. |
- Berggren, Björn, et al.
(författare)
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Innovative solution for heat recovery of ventilation air in older apartment buildings - with low intervention affecting the residents
- 2013
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Ingår i: ; , s. 428-438
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Konferensbidrag (refereegranskat)abstract
- Buildings today account for 40% of the world’s primary energy use and 24% of the greenhouse gas emissions. Reducing the energy use in buildings is an important measures to reduce energy dependency and greenhouse gas emissions. In Sweden, there are roughly 2 500 000 dwellings in multifamily houses and single family houses. There is a need to address the energy use within the existing dwellings; especially within multifamily buildings constructed 1960-1975, which accounts for almost one million dwellings or roughly 40 % of the dwelling stock in Sweden. There are good examples of energy renovations of buildings, reducing the energy use by more than 50 %. To reach the energy savings; balanced ventilation with heat recovery was a necessary measure in all projects. However, in all projects; loss of ceiling height in parts of the apartments is a consequence of the measure. Furthermore, it required the residents to temporary move during installment in the majority of the projects. The purpose of this study is to investigate the potential of using a heat exchanger, suitable for natural ventilation, exhaust air ventilation and hybrid ventilation, for installment in the existing building stock in Sweden. A qualitative and quantitative comparison is carried out; comparing mechanical exhaust air ventilation, balanced mechanical ventilation with heat recovery and the heat exchanger suitable for natural ventilation, exhaust air ventilation and hybrid ventilation. The qualitative analysis compares the advantages and disadvantages of the different ventilation system. The quantitative part investigates the potential energy savings and a potential quantity of dwellings where heat recovery may be installed. By installing heat recovery, energy used for space heating may be reduced by roughly 25%. Combining installment of heat recovery with improvement of the building envelope may reduce the energy demand for heating by roughly 75 %. Heat recovery should be able to install in roughly 80 % of the dwellings in the existing dwelling stock, built before 1980.
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| 4. |
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| 5. |
- Berggren, Björn, et al.
(författare)
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Normalisation of Measured Energy Use in Buildings — Need for a Review of the Swedish Regulations
- 2019
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Ingår i: Cold Climate HVAC 2018. CCC 2018. - Cham : Springer International Publishing. - 9783030006617 - 9783030006624 ; , s. 995-995
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Konferensbidrag (refereegranskat)abstract
- Normalisation of measured energy use in buildings is important in order to verify their performance in user phase. Two methods for normalisation have been presented in Sweden, static and dynamic normalisation. The static normalisation considers deviating hot water use, indoor temperature, internal loads and external climate. The dynamic normalisation is based on repeated simulation, meaning that the initial simulation, carried out during the design phase, is repeated with updated conditions regarding actual use of the building and exterior climate. The ratio between the first and second simulation is used as a factor for normalisation. A pre-study has been initiated in Sweden to enable further development of the two methods. This paper present the two methods, the initiated pre-study, and some early findings. The early findings show that there is need for further development of the methods presented.
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| 6. |
- Bergman, Svante
(författare)
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Bit loading and precoding for MIMO communication systems
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis considers the joint design of bit loading, precoding and receive filters for a multiple-input multiple-output (MIMO) digital communication system. Both the transmitter and the receiver are assumed to know the channel matrix perfectly. It is well known that, for linear MIMO transceivers, orthogonal transmission (i.e., diagonalization of the channel matrix) is optimal for some criteria such as maximum mutual information. It has been shown that if the receiver uses the linear minimum mean squared error (MMSE) detector, the optimal transmission strategy is to perform bit loading on orthogonal subchannels. In the first part of the thesis, we consider the problem of designing the transceiver in order to minimize the probability of error given maximum likelihood (ML) detection. A joint bit loading and linear precoder design is proposed that outperforms the optimal orthogonal transmission. The design uses lattice invariant operations to transform the channel matrix into a lattice generator matrix with large minimum distance separation at a low price in terms of transmit power. With appropriate approximations, it is shown that this corresponds to selecting lattices with good sphere-packing properties. An algorithm for this power minimization is presented along with a lower bound on the optimization. Apparently, given the optimal ML detector, orthogonal subchannels are (in general) suboptimal. The ML detector may suffer from high computational complexity, which motivates the use of the suboptimal but less complex MMSE detector. An intermediate detector in terms of complexity and performance is the decision feedback (DF) detector. In the second part of the thesis, we consider the problem of joint bit loading and precoding assuming the DF detector. The main result shows that for a DF MIMO transceiver where the bit loading is jointly optimized with the transceiver filters, orthogonal transmission is optimal. As a consequence, inter-symbol interference is eliminated and the DF part of the receiver is actually not required, only the linear part is needed. The proof is based on a relaxation of the discrete set of available bit rates on the individual subchannels to the set of positive real numbers. In practice, the signal constellations are discrete and the optimal relaxed bit loading has to be rounded. It is shown that the loss due to rounding is small, and an upper bound on the maximum loss is derived. Numerical results are presented that confirm the theoretical results and demonstrate that orthogonal transmission and the truly optimal DF design perform almost equally well. An algorithm that makes the filter design problem especially easy to solve is presented. As a byproduct from the work on decision feedback detectors we also present some work on the problem of optimizing a Schur-convex objective under a linearly shifted, or skewed, majorization constraint. Similar to the case with a regular majorization constraint, the solution is found to be the same for the entire class of cost functions. Furthermore, it is shown that the problem is equivalent to identifying the convex hull under a simple polygon defined by the constraint parameters. This leads to an algorithm that produces the exact optimum with linear computational complexity. As applications, two unitary precoder designs for MIMO communication systems that use heterogenous signal constellations and employ DF detection at the receiver are presented.
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| 7. |
- Bernardo, Ricardo, et al.
(författare)
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Measurements of the Electrical Incidence Angle Modifiers of an Asymmetrical Photovoltaic/Thermal Compound Parabolic Concentrating-Collector
- 2013
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Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 5, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmet-rical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maxi-mum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.
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| 8. |
- Bernardo, Ricardo, et al.
(författare)
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Measurements of the Electrical Incidence Angle Modifiers of an Asymmetrical Photovoltaic/Thermal Compound Parabolic Concentrating-Collector
- 2013
-
Ingår i: Engineering. - 1947-394X. ; 5:1B, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- Reflector edges, sharp acceptance angles and by-pass diodes introduce large variations in the electrical performance of asymmetrical concentrating photovoltaic/thermal modules over a short incidence angle interval. It is therefore important to quantify these impacts precisely. The impact on the electrical performance of the optical properties of an asymmetrical photovoltaic/thermal CPC-collector was measured in Maputo, Mozambique. The measurements were carried out with the focus on attaining a high resolution incidence angle modifier in both the longitudinal and transversal directions, since large variations were expected over small angle intervals. A detailed analysis of the contribution of the diffuse radiation to the total output was also carried out. The solar cells have an electrical efficiency of 18% while the maximum measured electrical efficiency of the collector was 13.9 % per active glazed area and 20.9 % per active cell area, at 25 °C. Such data make it possible to quantify not only the electrical performance for different climatic and operating conditions but also to determine potential improvements to the collector design. The electrical output can be increased by a number of different measures, e.g. removing the outermost cells, turning the edge cells 90°, dividing each receiver side into three or four parts and directing the tracking, when used, along a north-south axis.
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| 9. |
- Bernardo, Ricardo, et al.
(författare)
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Performance Evaluation of a High Solar Fraction CPC-Collector System
- 2011
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Ingår i: Journal of Environment and Engineering. - : Japan Society of Mechanical Engineers. - 1880-988X. ; 6:3, s. 680-692
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Tidskriftsartikel (refereegranskat)abstract
- One of the most important goals on solar collector development is to increase the system’s annual performance without increasing overproduction. The studied collector is formed by a compound parabolic reflector which decreases the collector optical efficiency during the summer period. Hence, it is possible to increase the collector area and thus, the annual solar fraction, without increasing the overproduction. Collector measurements were fed into a validated TRNSYS collector model which estimates the solar fraction of the concentrating system and also that of a traditional flat plate collector, both for domestic hot water production. The system design approach aims to maximise the collector area until an annual overproduction limit is reached. This is defined by a new deterioration factor that takes into account the hours and the collector temperature during stagnation periods. Then, the highest solar fraction achieved by both systems was determined. The results show that, at 50° tilt in Lund, Sweden, the concentrating system achieves 71% solar fraction using 17 m2 of collector area compared to 66% solar fraction and 7 m2 of a flat plate collector system. Thus, it is possible to install 2.4 times more collector area and achieve a higher solar fraction using the load adapted collector. However, the summer optical efficiency reduction was proven to be too abrupt. If the reflector geometry is properly design, the load adapted collector can be a competitive solution in the market if produced in an economical way.
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| 10. |
- Bertini, Ivano, et al.
(författare)
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Search for satellites near (21) Lutetia using OSIRIS/Rosetta images
- 2012
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 66:1, s. 64-70
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Tidskriftsartikel (refereegranskat)abstract
- On 2010 July 10 the ESA Rosetta mission flew by the large asteroid (21) Lutetia. One of the scientific goals of the onboard OSIRIS instrument was the search for satellites of the asteroid, with more than 20 images specifically dedicated to this topic. An observational campaign was devised with a selection of filters and exposure times tailored to maximize the possibility of detecting small companions and determining their bound orbits. Data were analyzed with suitable methods to remove cosmic ray hits and known background objects, in order to search for persistent detections of potential interesting flux sources. We found no unambiguous detections of a satellite larger than similar to 160 m inside the entire sphere of gravitational influence. Our search confirmed the absence of bound companions larger than similar to 30 m inside 20 primary radii. These limits are a factor of similar to 30 smaller than the values reported so far from large ground-based telescopes using adaptive optics and from the Hubble Space Telescope.
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| 11. |
- Bertini, I., et al.
(författare)
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Search for satellites near comet 67P/Churyumov-Gerasimenko using Rosetta/OSIRIS images
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583
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Tidskriftsartikel (refereegranskat)abstract
- Context. The European Space Agency Rosetta mission reached and started escorting its main target, the Jupiter-family comet 67P/Churyumov-Gerasimenko, at the beginning of August 2014. Within the context of solar system small bodies, satellite searches from approaching spacecraft were extensively used in the past to study the nature of the visited bodies and their collisional environment. Aims. During the approaching phase to the comet in July 2014, the OSIRIS instrument onboard Rosetta performed a campaign aimed at detecting objects in the vicinity of the comet nucleus and at measuring these objects' possible bound orbits. In addition to the scientific purpose, the search also focused on spacecraft security to avoid hazardous material in the comet's environment. Methods. Images in the red spectral domain were acquired with the OSIRIS Narrow Angle Camera, when the spacecraft was at a distance between 5785 km and 5463 km to the comet, following an observational strategy tailored to maximize the scientific outcome. From the acquired images, sources were extracted and displayed to search for plausible displacements of all sources from image to image. After stars were identified, the remaining sources were thoroughly analyzed. To place constraints on the expected displacements of a potential satellite, we performed Monte Carlo simulations on the apparent motion of potential satellites within the Hill sphere. Results. We found no unambiguous detections of objects larger than similar to 6 m within similar to 20 km and larger than similar to 1 m between similar to 20 km and similar to 110 km from the nucleus, using images with an exposure time of 0.14 s and 1.36 s, respectively. Our conclusions are consistent with independent works on dust grains in the comet coma and on boulders counting on the nucleus surface. Moreover, our analysis shows that the comet outburst detected at the end of April 2014 was not strong enough to eject large objects and to place them into a stable orbit around the nucleus. Our findings underline that it is highly unlikely that large objects survive for a long time around cometary nuclei.
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| 12. |
- Blennow, Kaj, 1958, et al.
(författare)
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No association between the alpha2-macroglobulin (A2M) deletion and Alzheimer's disease, and no change in A2M mRNA, protein, or protein expression.
- 2000
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Ingår i: Journal of neural transmission (Vienna, Austria : 1996). - : Springer Science and Business Media LLC. - 0300-9564 .- 1435-1463. ; 107:8-9, s. 1065-79
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Tidskriftsartikel (refereegranskat)abstract
- A polymorphism consisting of a deletion near the 5' splice site of exon 18 on the alpha2-macroglobulin (A2M) gene (A2M-2) has been suggested to be associated with Alzheimer's disease (AD) in family-based studies. We studied the A2M-2 allele together with the ApoE alleles in a large series on patients with AD (n = 449) and age-matched controls (n = 349). Neuropathologically confirmed diagnoses were available in 199 cases (94 AD and 107 control cases). We found no increase in A2M-2 genotype or allele frequencies in AD (27.5% and 14.6%) versus controls (26.4% and 14.9%). In contrast, a marked increase (p < 0.0001) in ApoE epsilon4 genotype or allele frequencies was found in AD (66.6% and 41.2%) as compared with controls (29.8% and 16.5%), suggesting sufficient statistical power in our sample. No relation was found between the A2M-2 and the ApoE epsilon4 allele. No change in A2M exon 17-18 mRNA size or sequence or A2M protein size was found in cases carrying the A2M-2 deletion, suggesting that there is no biological consequences of the A2M intronic deletion. No change in A2M protein level in cerebrospinal fluid was found in AD, suggesting that the A2M-2 allele does not effect the A2M protein expression in the brain. The lack of an association between the A2M-2 allele and AD in the present study, and the lack of abnormalities in the A2M mRNA or protein suggest that the A2M-2 allele is not associated with AD.
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| 13. |
- Blum, J., et al.
(författare)
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The physics of protoplanetesimal dust agglomerates : I. Mechanical properties and relations to primitive bodies in the solar system
- 2006
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 652:2, s. 1768-1781
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Tidskriftsartikel (refereegranskat)abstract
- We present laboratory experiments on the formation of macroscopic dust aggregates. The centimeter-sized highly porous bodies are produced by random ballistic deposition from individual micrometer-sized dust particles. We find packing densities between 0.07 and 0.15 for uncompressed samples, dependent on the shape and size distribution of the constituent dust grains. Impacts into these bodies are simulated by uniaxial compression experiments. We find that the maximum compression, equivalent to the highest protoplanetary impact velocities of similar to 50ms(-1), increases the packing density to 0.20-0.33. Tensile strength measurements with our laboratory samples yield values in the range 200-1100 Pa for slightly compressed samples. We review packing densities and tensile strengths found for primitive solar system bodies, e. g., for comets, primitive meteorites, and meteoroids. We find a consistency between packing densities and tensile strengths of our laboratory samples with those from cometary origin.
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| 14. |
- Bodewits, D., et al.
(författare)
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Changes in the physical environment of the inner coma of 67p/churyumov-gerasimenko with decreasing heliocentric distance
- 2016
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Ingår i: Astronomical Journal. - : IOP PUBLISHING LTD. - 0004-6256 .- 1538-3881. ; 152:5
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Tidskriftsartikel (refereegranskat)abstract
- The Wide Angle Camera of the OSIRIS instrument on board the Rosetta spacecraft is equipped with several narrow-band filters that are centered on the emission lines and bands of various fragment species. These are used to determine the evolution of the production and spatial distribution of the gas in the inner coma of comet 67P with time and heliocentric distance, here between 2.6 and 1.3 au pre-perihelion. Our observations indicate that the emission observed in the OH, OI, CN, NH, and NH2 filters is mostly produced by dissociative electron impact excitation of different parent species. We conclude that CO2 rather than H2O is a significant source of the [OI] 630 nm emission. A strong plume-like feature observed in the CN and OI filters is present throughout our observations. This plume is not present in OH emission and indicates a local enhancement of the CO2/H2O ratio by as much as a factor of 3. We observed a sudden decrease in intensity levels after 2015 March, which we attribute to decreased electron temperatures in the first few kilometers above the surface of the nucleus.
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| 15. |
- Carlsson, Jessica, 1984-, et al.
(författare)
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A miRNA expression signature that separates between normal and malignant prostate tissues
- 2011
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Ingår i: Cancer Cell International. - : BioMed Central (BMC). - 1475-2867. ; :11, s. 14-
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundMicroRNAs (miRNAs) constitute a class of small non-coding RNAs that post-transcriptionally regulate genes involved in several key biological processes and thus are involved in various diseases, including cancer. In this study we aimed to identify a miRNA expression signature that could be used to separate between normal and malignant prostate tissues.ResultsNine miRNAs were found to be differentially expressed (p <0.00001). With the exception of two samples, this expression signature could be used to separate between the normal and malignant tissues. A cross-validation procedure confirmed the generality of this expression signature. We also identified 16 miRNAs that possibly could be used as a complement to current methods for grading of prostate tumor tissues.ConclusionsWe found an expression signature based on nine differentially expressed miRNAs that with high accuracy (85%) could classify the normal and malignant prostate tissues in patients from the Swedish Watchful Waiting cohort. The results show that there are significant differences in miRNA expression between normal and malignant prostate tissue, indicating that these small RNA molecules might be important in the biogenesis of prostate cancer and potentially useful for clinical diagnosis of the disease.
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| 16. |
- Cremonese, G., et al.
(författare)
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Photometry of dust grains of comet 67P and connection with nucleus regions
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 588
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Multiple pairs of high-resolution images of the dust coma of comet 67P/Churyumov-Gerasimenko have been collected by OSIRIS onboard Rosetta allowing extraction and analysis of dust grain tracks. Methods. We developed a quasi automatic method to recognize and to extract dust tracks in the Osiris images providing size, FWHM and photometric data. The dust tracks characterized by a low signal-to-noise ratio were checked manually. We performed the photometric analysis of 70 dust grain tracks observed on two different Narrow Angle Camera images in the two filters F24 and F28, centered at lambda = 480.7 nm and at lambda = 743.7 nm, respectively, deriving the color and the reddening of each one. We then extracted several images of the nucleus observed with the same filters and with the same phase angle to be compared with the dust grain reddening. Results. Most of the dust grain reddening is very similar to the nucleus values, confirming they come from the surface or subsurface layer. The histogram of the dust grain reddening has a secondary peak at negative values and shows some grains with values higher than the nucleus, suggesting a different composition from the surface grains. One hypothesis comes from the negative values point at the presence of hydrated minerals in the comet.
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| 17. |
- Davidsson, Björn, et al.
(författare)
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A practical tool for simulating the presence of gas comae in thermophysical modeling of cometary nuclei
- 2004
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035. ; 168:1, s. 163-185
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Tidskriftsartikel (refereegranskat)abstract
- A longstanding problem in thermophysical modeling of cometary nuclei has been to accurately formulate the boundary conditions at the nucleus/coma interface. A correct treatment of the problem, where the Knudsen layer gas just above the cometary surface (which is not in thermodynamic equilibrium) is modeled in parallel with the nucleus, is extremely time-consuming and has so far been avoided. Instead, simplifying assumptions regarding the coma properties are used, e.g., the surface gas density is assumed equal to zero or set to the local saturation value, and the coma backflux is neglected or given some realistic but approximate value. The resulting inaccuracy regarding the exchange of mass, energy, and momentum between the nucleus and the coma, may introduce significant errors in the calculated nucleus temperature profiles, gas production rates, and momentum transfer efficiencies. In this paper, we present a practical, accurate, and time-efficient tool which makes it possible to consider the nucleus and the innermost coma of a comet (the former assumed to consist of a porous mixture of crystalline water ice and dust) as a coupled, physically consistent system. The tool consists of interpolation tables for the surface gas density and pressure, the recondensing coma backflux, and the cooling energy flux due to diffusely scattered coma molecules. The tables cover a wide range of surface temperatures and sub-surface temperature profiles, and can be used to improve the boundary conditions used in thermophysical models. The interpolation tables have been obtained by calculating the transmission distribution functions of gas emerging from sublimating porous ice/dust mixtures with various temperature profiles, which then are used as source functions in a Direct Simulation Monte Carlo model of inelastic intermolecular collisions in the Knudsen layer.
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| 18. |
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| 19. |
- Davidsson, Björn J. R.
(författare)
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Comet Knudsen layers
- 2008
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Ingår i: Space Science Reviews. - : Springer Science and Business Media LLC. - 0038-6308 .- 1572-9672. ; 138:1-4, s. 207-223
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews some important results about Knudsen layers obtained in theoretical gas kinetics research in the last few decades, focusing on the weak and strong evaporation problems in two-surface, half-space, and spherical geometries. Furthermore, the application of such results in cometary science is reviewed. In order to illustrate some properties of the half-space evaporation problem for water ice surfaces at temperatures relevant for active comets, a number of numerical Direct Simulation Monte Carlo calculations are presented.
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| 20. |
- Davidsson, Björn J. R., et al.
(författare)
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Gas kinetics and dust dynamics in low-density comet comae
- 2010
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 210:1, s. 455-471
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Tidskriftsartikel (refereegranskat)abstract
- Extensive regions of low-density cometary comae are characterized by important deviations from the Maxwell-Boltzmann velocity distribution, i.e. breakdown of thermodynamic equilibrium. The consequences of this on the shapes of emission and absorption lines, and for the acceleration of solid bodies due to gas drag, have rarely been investigated. These problems are studied here to aid in the development of future coma models, and in preparation for observations of Comet 67P/Churyumov-Gerasimenko from the ESA Rosetta spacecraft. Two topics in particular, related to Rosetta, are preparation for in situ observations of water, carbon monoxide, ammonia, and methanol emission lines by the mm/sub-mm spectrometer MIRO, as well as gas drag forces on dust grains and on the Rosetta spacecraft itself. Direct Simulation Monte Carlo (DSMC) modeling of H2O/CO mixtures in spherically symmetric geometries at various heliocentric distances are used to study the evolution of the (generally non-Maxwellian) velocity distribution function throughout the coma. Such distribution functions are then used to calculate Doppler broadening profiles and drag forces. It is found that deviation from thermodynamic equilibrium indeed is commonplace, and already at 2.5 AU from the Sun the entire comet coma displays manifestations of such breakdown, e.g., non-equal partitioning of energy between kinetic and rotational modes, causing substantial differences between translational and rotational temperatures. We exemplify how deviations from thermodynamic equilibrium affect the properties of Doppler broadened line profiles. Upper limits on the size of liftable dust grains as well as terminal grain velocities are presented. Furthermore, it is demonstrated that the drag-to-gravity force ratio is likely to decrease with decreasing cometocentric distance, which may be of relevance both for Rosetta and for the lander probe Philae.
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| 21. |
- Davidsson, Björn J. R., et al.
(författare)
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Interpretation of thermal emission. I. The effect of roughness for spatially resolved atmosphereless bodies
- 2015
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 252, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Spacecraft observations of atmosphereless Solar System bodies, combined with thermophysical modeling, provide important information about the thermal inertia and degree of surface roughness of these bodies. The thermophysical models rely on various methods of generating topography, the most common being the concave spherical segment. We here compare the properties of thermal emission for a number of different topographies - concave spherical segments, random Gaussians, fractals and parallel sinusoidal trenches - for various illumination and viewing geometries, degrees of surface roughness and wavelengths. We find that the thermal emission is strongly dependent on roughness type, even when the degrees of roughness are identical, for certain illumination and viewing geometries. The systematic usage of any single topography model may therefore bias determinations of thermal inertia and level of roughness. We outline strategies that may be employed during spacecraft observations to disentangle thermal inertia, level of roughness and type of topography. We also compare the numerically complex and time consuming full-scale thermophysical models with a simplified statistical approach, which is fairly easy to implement and quick to run. We conclude that the simplified statistical approach is similar to thermophysical models for cases tested here, which enables the user to analyze huge amounts of spectral data at a low numerical cost.
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| 22. |
- Davidsson, Björn J. R., et al.
(författare)
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Nucleus properties of Comet 9P/Tempel 1 estimated from non-gravitational force modeling
- 2007
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 187:1, s. 306-320
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Tidskriftsartikel (refereegranskat)abstract
- The nucleus mass and bulk density of Comet 9P/Tempel 1 have been estimated by utilizing the non-gravitational force modeling technique. Here, the water production rates and non-gravitational perturbations of the orbit are calculated for a large number of model nuclei with different surface ice distribution patterns. By requiring that the empirical water production rate curve is reproduced, a subset of model nuclei are selected, for which masses are calculated by demanding that empirical non-gravitational changes of the orbital period and in the longitude of perihelion (per revolution) are reproduced. We obtain a mass M=5.8(±1.6)×1013 kg, and a bulk density , which compares very well with measurements made by the Deep Impact Science Team. The main goal of the current work is therefore to demonstrate functionality of an indirect method, i.e., mass estimation through non-gravitational force modeling, by comparing such results to ground truth data. Furthermore, the thermal inertia of active areas is estimated as 30–100 MKS, using a comparatively realistic thermophysical model (although a value in the range 100–350 MKS is obtained with a more simple model). An active area fraction of 3% is predicted, and these areas are probably confined to the northern hemisphere, being located close to the cometary equator.
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| 23. |
- Davidsson, Björn J. R., et al.
(författare)
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Physical properties of morphological units on Comet 9P/Tempel 1 derived from near-IR Deep Impact spectra
- 2009
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 201:1, s. 335-357
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we analyze near-infrared thermal emission spectra of the spatially resolved nucleus Of Comet 9P/Tempel 1 obtained by the NASA spacecraft Deep Impact. Maps of spectral reddening. the product X' between the beaming function and directional emissivity, as well as Suit ace temperature are constructed. Thermophysical modeling is used to estimate the degree of small scale surface toughness and thermal inertia by detailed reproduction of the empirical temperature map. Mie and Hapke theories are Used in combination with numerically Calculated beaming functions to analyze the X' trial and place constraints oil composition and grain size of the Surface material. We show that it is absolutely mandatory to include small scale Surface roughness in thermophysical modeling of this object, since the resulting self treating is vital for reproducing the measured temperatures. A small scale self heating parameter in the range 0.6 <= xi <= 0.75 is common, but smoother areas where 0.2 <= xi <= 0.3 are also found. Contrary to models neglecting small scale surface roughness, we find that the thermal inertia of Comet 9P/Tempel 1 generally is high (1000-3000 J m(-1) K-1 s(-1/2)). although it may be substantially lower (40-380 Jm(-2) K-1 s(-1/2)) in specific areas. We obtain a disk-averaged reddening of 3.5% kA(-1), with statistically significant local variations around that value on a +/- 1.0% kA(-1) level. vast regions appear covered by small (similar to 0.1 mu m) highly absorbing grains such as carbon or iron-rich silicates. Other regions appear dominated by somewhat larger (similar to 0.5 mu m) and/or less absorbing grains such as troilite or magnesium-rich silicates. Surface variations in reddening, roughness, thermal inertia, composition and/or grain size are moderately to strongly correlated to the locations of morphological units oil the surface. The existence of morphological units with differing physical properties may be primordial. hence reflecting a diversity in the building block cometesimals, or resulting front evolutionary processes. (c) 2009 Elsevier Inc. All rights reserved.
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| 24. |
- Davidsson, Björn J. R., et al.
(författare)
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Surface roughness and three-dimensional heat conduction in thermophysical models
- 2014
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 243, s. 58-77
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Tidskriftsartikel (refereegranskat)abstract
- A thermophysical model is presented that considers surface roughness, cast shadows, multiple or single scattering of radiation, visual and thermal infrared self heating, as well as heat conduction in one or three dimensions. The code is suitable for calculating infrared spectral energy distributions for spatially resolved or unresolved minor Solar System bodies without significant atmospheres or sublimation, such as the Moon, Mercury, asteroids, irregular satellites or inactive regions on comet nuclei. It is here used to explore the effects of surface roughness on spatial scales small enough for heat conduction to erase lateral temperature gradients. Analytically derived corrections to one-dimensional models that reproduce the results of three-dimensional modeling are presented. We find that the temperature of terrains with such small-scale roughness is identical to that of smooth surfaces for certain types of topographies and non-scattering material. However, systematic differences between smooth and rough terrains are found for scattering materials, or topographies with prominent positive relief. Contrary to common beliefs, the roughness on small spatial scales may therefore affect the thermal emission of Solar System bodies.
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| 25. |
- Davidsson, Björn J. R., et al.
(författare)
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Thermal inertia and surface roughness of Comet 9P/Tempel 1
- 2013
-
Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 224:1, s. 154-171
-
Tidskriftsartikel (refereegranskat)abstract
- Re-calibrated near-infrared spectroscopy of the resolved nucleus of Comet 9P/Tempel 1 acquired by the Deep Impact spacecraft has been analyzed by utilizing the post-Stardust-NExT nucleus shape model and spin pole solution, as well as a novel thermophysical model that explicitly accounts for small-scale surface roughness and thermal inertia. We find that the thermal inertia varies measurably across the surface, and that thermal emission from certain regions only can be reproduced satisfactory if surface roughness is accounted for. Particularly, a scarped/pitted terrain that experienced morning sunrise during the flyby is measurably rough (Hapke mean slope angle similar to 45 degrees) and has a thermal inertia of at most 50J m(-2) K-1 s(-1/2), but probably much lower. However, thick layered terrain and thin layered terrain experiencing local noon during the flyby have a substantially larger thermal inertia, reaching 150J m(-2) K-1 s(-1/2) if the surface is as rough as the scarped/pitted terrain, but 200J m(-2) K-1 s(-1/2) if the terrain is considered locally flat. Furthermore, the reddening of the nucleus near-infrared 1.5-2.2 gm spectrum varies between morphological units, being reddest for thick layered terrain (median value 3.4% k angstrom(-1)) and most neutral for the smooth terrain known to contain surface water ice (median value 3.1% k angstrom(-1)). Thus, Comet 9P/Tempel 1 is heterogeneous in terms of both thermophysical and optical properties, due to formation conditions and/or post-formation processing.
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| 26. |
- Davidsson, Björn J. R., et al.
(författare)
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Thermal Inertia and Surface Roughness of Comet 9P/Tempel 1 Derived from Recalibrated Deep Impact NIR Spectroscopy
- 2011
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Ingår i: EPSC-DPS Joint Meeting 2011. ; , s. 221-
-
Konferensbidrag (refereegranskat)abstract
- On July 4, 2005, the HRI-IR instrument onboard the Deep Impact spacecraft (NASA/Univ. of Maryland) acquired the first ever near-infrared spectra of a fully resolved comet nucleus, 9P/Tempel 1. Early attempts to estimate the thermal inertia of the surface material were inconclusive, due to negligence of small-scale surface roughness in the thermophysical models used to analyze the spectra. Following a substantial recalibration of the original dataset, we now reconsider the 9P/Tempel 1 spectra, using more realistic thermophysical models. In addition to largescale nucleus irregularity, these models now explicitly consider small-scale roughness and related phenomena such as shadowing and IR self heating. Furthermore, 3D heat conduction can be utilized when topographic features are similar in size to the thermal skin depth, or smaller. Estimates of the thermal inertia, degree of small-scale roughness and their levels of variation across the nucleus are presented.
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Davidsson, Björn, et al.
(författare)
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On the light-absorbing surface layer of cometary nuclei : I. Radiative transfer
- 2002
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035. ; 156:1, s. 223-248
-
Tidskriftsartikel (refereegranskat)abstract
- A small but increasing volume of observations of cometary nuclei hasaccumulated during the last two decades. This development is acceleratingwith upcoming space missions such as Stardust, Contour, and Rosetta. Inresponse to the growing need for a theoretical understanding of opticalproperties of cometary nuclei, we have calculated synthetic reflectancespectra in the 0.2-2.0 micrometer wavelength region, photometriccolors in the Johnson-Kron-Cousins UBVRI system, and visual geometricalbedos, for a large number of porous ice-dust mixtures with differentcomposition, regolith grain sizes and grain morphologies, such ascore-mantle grains, dense clusters of such grains, and large irregularparticles with internal scatterers. The calculations are based on Mie theory,the Discrete Dipole Approximation, Hapke theory, and a numerical solutionof the equation of radiative transfer in particulate media. In addition,wavelength-integrated directional-hemispherical albedos and flux attenuation profiles in theregolith as functions of depth, have been calculated in order to improve theenergy budget and treatment of energy boundary conditions in thermal modelsof cometary nuclei.Our results are compared with spectra and colors of observed cometary nuclei.Our main conclusions are that only regolith consisting of relatively largecore-mantle grains, or clusters of smaller core-mantle grains, are capableof reproducing the red colors seen in comets; that ice-dust mixturesactually can be darker than ice-free regolith under certain circumstances;and that solar radiation sometimes penetrates to a depth that is comparableto the region in which diurnal temperature variations occur.
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| 31. |
- Davidsson, Björn, et al.
(författare)
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On the light-absorbing surface layer of cometary nuclei : II. Thermal modeling
- 2002
-
Ingår i: Icarus. - : Elsevier BV. - 0019-1035. ; 159:1, s. 239-258
-
Tidskriftsartikel (refereegranskat)abstract
- The classical way to treat absorption of solar light in thermophysical modelling of cometary nuclei (and other ice-rich bodies such as jovian satellites), has been to assume complete opaqueness of the surface material. However, as shown by Davidsson and Skorov (2002), substantial light penetration can occur in porous ice even if it is very dusty, implying that gradual absorption of energy in a surface layer should be accounted for.We present a thorough comparison between a surface energy absorption model and a layer energy absorption model, for various combinations of heliocentric distances, conductivities, opacities, pore sizes and rotational periods relevant for cometary nuclei, by fully solving the coupled differential equations of heat transfer and gas diffusion. We find substantial differences between the models in terms of gas production rate, thermal lag angle, surface temperature, and the origin of coma molecules. For example, the surface energy absorption model overestimates the total gas production by a factor 2-7, underestimates the lag angle by a factor 2-3, and places the origin of coma molecules at the surface, instead of the near--surface interior.
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| 32. |
- Davidsson, Björn, et al.
(författare)
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Orbital elements of the material surrounding comet 67P/Churyumov-Gerasimenko
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583
-
Tidskriftsartikel (refereegranskat)abstract
- Context. We investigate the dust coma within the Hill sphere of comet 67P/Churyumov-Gerasimenko. Aims. We aim to determine osculating orbital elements for individual distinguishable but unresolved slow-moving grains in the vicinity of the nucleus. In addition, we perform photometry and constrain grain sizes. Methods. We performed astrometry and photometry using images acquired by the OSIRIS Wide Angle Camera on the European Space Agency spacecraft Rosetta. Based on these measurements, we employed standard orbit determination and orbit improvement techniques. Results. Orbital elements and effective diameters of four grains were constrained, but we were unable to uniquely determine them. Two of the grains have light curves that indicate grain rotation. Conclusions. The four grains have diameters nominally in the range 0.14-0.50 m. For three of the grains, we found elliptic orbits, which is consistent with a cloud of bound particles around the nucleus. However, hyperbolic escape trajectories cannot be excluded for any of the grains, and for one grain this is the only known option. One grain may have originated from the surface shortly before observation. These results have possible implications for the understanding of the dispersal of the cloud of bound debris around comet nuclei, as well as for understanding the ejection of large grains far from the Sun.
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| 33. |
- Davidsson, Björn
(författare)
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The bulk density of cometary nuclei
- 2006
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Ingår i: Advances in Geosciences. - : World Scientific Publishing, Singapore. - 9812569839
-
Bokkapitel (refereegranskat)
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| 34. |
- Davidsson, Björn, et al.
(författare)
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The primordial nucleus of comet 67P/Churyumov-Gerasimenko
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
-
Tidskriftsartikel (refereegranskat)abstract
- Context. We investigate the formation and evolution of comet nuclei and other trans-Neptunian objects (TNOs) in the solar nebula and primordial disk prior to the giant planet orbit instability foreseen by the Nice model. Aims. Our goal is to determine whether most observed comet nuclei are primordial rubble-pile survivors that formed in the solar nebula and young primordial disk or collisional rubble piles formed later in the aftermath of catastrophic disruptions of larger parent bodies. We also propose a concurrent comet and TNO formation scenario that is consistent with observations. Methods. We used observations of comet 67P/Churyumov-Gerasimenko by the ESA Rosetta spacecraft, particularly by the OSIRIS camera system, combined with data from the NASA Stardust sample-return mission to comet 81P/Wild 2 and from meteoritics; we also used existing observations from ground or from spacecraft of irregular satellites of the giant planets, Centaurs, and TNOs. We performed modeling of thermophysics, hydrostatics, orbit evolution, and collision physics. Results. We find that thermal processing due to short-lived radionuclides, combined with collisional processing during accretion in the primordial disk, creates a population of medium-sized bodies that are comparably dense, compacted, strong, heavily depleted in supervolatiles like CO and CO2; they contain little to no amorphous water ice, and have experienced extensive metasomatism and aqueous alteration due to liquid water. Irregular satellites Phoebe and Himalia are potential representatives of this population. Collisional rubble piles inherit these properties from their parents. Contrarily, comet nuclei have low density, high porosity, weak strength, are rich in supervolatiles, may contain amorphous water ice, and do not display convincing evidence of in situ metasomatism or aqueous alteration. We outline a comet formation scenario that starts in the solar nebula and ends in the primordial disk, that reproduces these observed properties, and additionally explains the presence of extensive layering on 67P/Churyumov-Gerasimenko (and on 9P/Tempel 1 observed by Deep Impact), its bi-lobed shape, the extremely slow growth of comet nuclei as evidenced by recent radiometric dating, and the low collision probability that allows primordial nuclei to survive the age of the solar system. Conclusions. We conclude that observed comet nuclei are primordial rubble piles, and not collisional rubble piles. We argue that TNOs formed as a result of streaming instabilities at sizes below similar to 400 km and that similar to 350 of these grew slowly in a low-mass primordial disk to the size of Triton, Pluto, and Eris, causing little viscous stirring during growth. We thus propose a dynamically cold primordial disk, which prevented medium-sized TNOs from breaking into collisional rubble piles and allowed the survival of primordial rubble-pile comets. We argue that comets formed by hierarchical agglomeration out of material that remained after TNO formation, and that this slow growth was a necessity to avoid thermal processing by short-lived radionuclides that would lead to loss of supervolatiles, and that allowed comet nuclei to incorporate similar to 3 Myr old material from the inner solar system.
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| 35. |
- Davidsson, Björn
(författare)
-
Thermophysical Modelling and Mechanical Stability of Cometary Nuclei
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Comets are the most primordial and least evolved bodies in the Solar System. As such, they are unique sources of information regarding the early history of the Solar System. However, little is known about cometary nuclei since they are very difficult to observe due to the obscuring coma. Indirect methods are therefore often used to extract knowledge about nucleus parameters such as size, shape, density, material strength, and rotational properties. For example, tidal and non-tidal splitting of cometary nuclei can provide important information about nuclear densities and material strengths, but only if the criteria for mechanical stability are well known. Masses and densities of cometary nuclei can also be obtained by studying orbital modifications due to non-gravitational forces, but only if the thermophysics of comets can be modelled accurately. A detailed investigation is made regarding the mechanical stability of small Solar System bodies. New expressions for the Roche distance are derived, as functions of the size, shape, density, material strength, rotational period, and spin axis orientation of a body. The critical rotational period for centrifugal breakup in free space is also considered, and the resulting formulae are applied to comets for which the size, shape and rotational period have been estimated observationally, in order to place constraints on their densities and material strengths. A new thermophysical model of cometary nuclei is developed, focusing on two rarely studied features - layer absorption of solar energy, and parallel modelling of the nucleus and innermost coma. Sophisticated modelling of radiative transfer processes and the kinetics of gas in thermodynamic non-equilibrium form the basis for this work. The new model is applied to Comet 19P/Borrelly, and its density is estimated by reproducing the non-gravitational changes of its orbit.
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| 36. |
- Davidsson, Henrik, et al.
(författare)
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Construction of laboratories for solar energy research in developing countries
- 2014
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Ingår i: Energy Procedia 57. - : Elsevier BV. - 1876-6102. ; 57:Energy Procedia 57, s. 982-988
-
Konferensbidrag (refereegranskat)abstract
- A large number of photovoltaic systems have been installed in developing countries around the world during numerous projects. The goal is often to improve the quality of life in rural areas often lacking electricity. Many of these installations provide important services such as lighting and charging of various devices. However, when the projects are finished, there is a large risk that maintenance is not carried out properly and that malfunctions are never repaired. This situation can leave an otherwise well- functioning system unusable. A key problem is that there are not enough trained technicians that can maintain and repair the system locally. One reason for this is the lack of practical education in many developing countries. Furthermore, the availability of spare parts is essential for long term effectiveness. During 2011 a group of researchers from Lund University in Sweden built a small scale laboratory in Maputo, Mozambique, with local researchers. The project was successful and today the laboratory functions both as a teaching facility and as a measurement station for solar energy research for licentiates, masters and Ph.D. students. The main goal now is to widen the project in order to incorporate more universities in developing countries. We are now looking for new interested partners in developing countries who believe that such a laboratory could strengthen their ability to teach practical work and to perform research at a local university. Partners for planning and executing the project are also needed.
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| 37. |
- Davidsson, Henrik, et al.
(författare)
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Energy use of buildings in relation to occupancy rates
- 2021
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Ingår i: Proceedings of the 8th International Building Physics Conference. - : IOP Publishing. ; :2069
-
Konferensbidrag (refereegranskat)abstract
- This paper presents basic data of the energy demand for district heating and plug loads logged by a building management system of an energy-efficient academic building located in Lund, Sweden. The data refers to the years 2019 and 2020 when occupancy varied significantly due to the Corona pandemic. The data shows that the building energy demand adapts poorly to fluctuating occupancy rates. With a possible increase of smart working in the future, building codes should account for more fluctuating occupancy rates in the modelling of the energy demand of buildings.
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| 38. |
- Davidsson, Henrik, et al.
(författare)
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Performance of a multifunctional PV/T hybrid solar window
- 2010
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Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X. ; 84:3, s. 365-372
-
Tidskriftsartikel (refereegranskat)abstract
- A building-integrated multifunctional PV/T solar window has been developed and evaluated. It is constructed of PV cells laminated on solar absorbers placed in a window behind the glazing. To reduce the cost of the solar electricity, tiltable reflectors have been introduced in the construction to focus radiation onto the solar cells. The reflectors render the possibility of controlling the amount of radiation transmitted into the building. The insulated reflectors also reduce the thermal losses through the window. A model for simulation of the electric and hot water production was developed. The model can perform yearly energy simulations where different features such as shading of the cells or effects of the glazing can be included or excluded. The simulation can be run with the reflectors in an active, up right, position or in a passive, horizontal, position. The simulation program was calibrated against measurements on a prototype solar window placed in Lund in the south of Sweden and against a solar window built into a single family house, Solgården, in Älvkarleö in the central part of Sweden. The results from the simulation shows that the solar window annually produces about 35% more electric energy per unit cell area compared to a vertical flat PV module.
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| 39. |
- Davidsson, Henrik, et al.
(författare)
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Performance of a multifunctional PV/T hybrid solar window
- 2008
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Ingår i: [Host publication title missing]. ; , s. 44-51
-
Konferensbidrag (refereegranskat)abstract
- A PV/T collector have been developed and evaluated at the department of Energy and Building Design at the Technical University of Lund, LTH in Sweden. The PV/T, a “multifunctional solar window” made of PV cells laminated on solar absorbers, is placed in a window behind the glazing. The solar window is built into a single family house, Solgården, in Älvkarleö outside Gävle in the eastern part of Sweden. To reduce the costs of the solar electricity, reflectors have been placed in the construction to focus the radiation onto the solar cells. In this way expensive solar cells can be replaced by considerably cheaper reflector material. The tiltable reflectors give the user a possibility to control the amount of radiation being transmitted into the building. The reflectors can also be used to reduce the thermal losses through the window. A model for electric and hot water production was developed. The simulation program, in Excel, can perform yearly energy simulations where different effects such as shading of the cells or the glazing effects can be included or excluded. The simulation can be run with the reflectors in an active, up right, position or with the reflectors in a passive, horizontal, position. The simulation program was calibrated against a prototype window placed in Lund in the south of Sweden and against the solar window in Solgården. The calculation model serves as a basis for the module written for the simulation program TRNSYS. A “TRNSYS-deck” was built and calibrated for the building Solgården. Yearly simulations of the energy balance for a house with the solar window was compared to simulations where the 16m2 solar window was replaced with an 8m2 normal window. The results show that the annual amount of auxiliary energy is lower with a developed solar window, including low-e coating on the glazing, compared to the normal window case. The developed solar window has considerable lower U-values than the existing solar window.
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| 40. |
- Davidsson, Henrik, et al.
(författare)
-
Performance of a multifunctional PV/T hybrid solar window
- 2008
-
Ingår i: EuroSun 2008 Proceedings.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A building-integrated multifunctional PV/T collector have been developed and evaluated. The PV/T solar window is constructed of PV cells laminated on solar absorbers and is placed in a window behind the glazing. To reduce the costs of the solar electricity, reflectors have been introduced in the construction to focus radiation onto the solar cells. The tiltable reflectors render a possibility to control the amount of radiation transmitted into the building. The insulated reflectors also reduce the thermal losses through the window. A model for simulation of the electric and hot water production was developed. The model can perform yearly energy simulations where different effects such as shading of the cells or effects of the glazing can be included or excluded. The simulation can be run with the reflectors in an active, up right, position or with the reflectors in a passive, horizontal, position. The simulation program was calibrated against measurements on a prototype solar window placed in Lund in the south of Sweden and against a solar window built into a single family house, Solgården, in Älvkarleö in the middle of Sweden. The results from the simulation shows that the solar window produces about 56% more electric energy per unit cell area compared to a vertical flat PV module.
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| 41. |
- Davidsson, Henrik, et al.
(författare)
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System analysis of a multifunctional PV/T hybrid solar window
- 2012
-
Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X. ; 86:3, s. 903-910
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe work presented in this article aims to investigate a PV/T hybrid solar window on a system level. A PV/T hybrid is an absorber on which solar cells have been laminated. The solar window is a PV/T hybrid collector with tiltable insulated reflectors integrated into a window. It simultaneously replaces thermal collectors, PV-modules and sunshade. The building integration lowers the total price of the construction since the collector utilizes the frame and the glazing in the window. When it is placed in the window a complex interaction takes place. On the positive side is the reduction of the thermal losses due to the insulated reflectors. On the negative side is the blocking of solar radiation that would otherwise heat the building passively. This limits the performance of the solar window since a photon can only be used once. To investigate the sum of such complex interaction a system analysis has to be performed. In this paper results are presented from such a system analysis showing both benefits and problems with the product. The building system with individual solar energy components, i.e. solar collector and PV modules, of the same size as the solar window, uses 1100 kW h less auxiliary energy than the system with a solar window. However, the solar window system uses 600 kW h less auxiliary energy than a system with no solar collector.
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| 42. |
- Davidsson, Henrik, et al.
(författare)
-
Utveckling av Byggnadsintegrerade Solenergisystem för Energieffektiva Hus
- 2008
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A PV/T collector has been developed and evaluated at the department of Energy and Building Design at the Technical University of Lund, LTH in Sweden. The PV/T, a “solar window” made of PV cells laminated on solar absorbers is placed in a window behind the glazing. The solar window is built into a single family house, Solgården, in Älvkarleö outside Gävle in the eastern part of Sweden. To reduce the costs of the solar electricity reflectors have been placed in the construction to focus light onto the solar cells. In this way expensive solar cells can be replaced by considerably cheaper reflector material. The tiltable reflectors give the user a possibility to control the amount of sunlight being let into the building. The reflectors can also be used to reduce the thermal losses through the window. A calculation model for electricity and hot water production was created. The simulation program, in Excel, can perform yearly energy simulations where different effects such as shading of the cells or the glazing effects can be included or excluded. The simulation can be run with the reflectors in an active, up right, position or with the reflectors in a passive, horizontal, position. The simulation programme was calibrated against a prototype window placed in Lund in the south of Sweden and against the solar window in Solgården Älvkarleö. The calculation model serves as a basis for the module written for the simulation program TRNSYS. A “TRNSYS-deck” was built and calibrated for the building Solgården. The energy balance for the system shows that the control of the reflectors is of great importance. A good control strategy for the reflectors can lower the annual energy demand and improve the indoor climate. A control mechanism that incorporates the indoor and outdoor temperatures can for instance decide to open the reflectors during summer nights to cool the building. Yearly simulations of the energy balance for a house with the solar window was compared to simulations where the 16 m2 solar window was replaced with a 8 m2 normal window. The results show the annual amount of auxiliary is lower with a developed solar window compared to the normal window case. The developed solar window has considerably lower U-values than the existing solar window. A simulation was run to investigate the over heating of the building using different control strategies for the reflectors. The simulation was also run for the normal window. The results show that the reflectors of the solar window work fine as a sun shade, keeping the overheating to a minimum. A normal window has to be supplemented with a sun shade of some kind to keep the over heating during the summer on an acceptable level. An Improvement of the solar window that can be of great importance is to add some sort of low-e coating on the glazing to reduce the U-value even further. However, it must be taken into account that the transmittance of the glazing will be affected in a negative way if low-e coating is added. Lower transmission means lower electricity and hot water production. Other improvements that can be made are better insulation of the reflector and the absorber. The most important way to improve the annual electricity production is to use better solar cells. Today cells of standard quality with an efficiency of about 16-17% can be obtained. The electric system at Solgården is built up around a battery bank that can be charged from the solar window, the Stirling generator or from the grid. To have continuous power for some time during a black out and also the relatively low fuse that is needed for the house are two advantages with this system. Simulations show that the day to day storage of electricity in the batteries evens out the power peaks from the load and the electric production, and that further storage is of limited use. Simulations show that the production of electric energy from a combination of solar cells and a Stirling generator is in good agreement with the load during the full year. Solgårdens two parallel electric systems, 230 V and 12 V, has many advantages such as electric security and low energy consumption. To save electric energy is of extra interest when solar cells are used as an energy source. Due to the high price for solar cells large energy saving investments ought to be made before a solar cell installation is economically interesting. To move the energy use from electricity to hot water use is profitable for a stand alone house since solar heating and bio fuel is considerably cheaper compared to solar electricity. Tumble driers, washing machines and dishwashers can for instance use a circulating hot water system instead of electricity in order to minimize the electric use. Normally the energy balance between produced electric energy and produced thermal energy is in better agreement if hot water is used instead of electric energy. Other important investments to make the electric usage more efficient are to use low energy light bulbs and modern kitchen appliances, pumps, fans and computers. This can save as much as 80% of the electricity compared to old standard techniques. Solgården is in practice working with the main fuses of the sizes of 3-4 A only. This can be accomplished because of the battery bank and since no equipment with a high current demand is connected to the power system. A high slope of the PV-modules has the advantage that the power during the summer is decreased. On the other hand a module tilt of 45° is to prefer both from an energy and a power view. A 45° tilted module gives a higher annual output in kWh per monitored kWp than a vertical module.
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| 43. |
- Davidsson, Lisa, et al.
(författare)
-
Ultrasound-assessed plaque occurrence in the carotid and femoral arteries are independent predictors of cardiovascular events in middle-aged men during 10 years of follow-up.
- 2009
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Ingår i: Atherosclerosis. - : Elsevier BV. - 1879-1484 .- 0021-9150.
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: To examine if plaques in the carotid and femoral arteries were associated with cardiovascular events during a 10-year follow-up independently of usual risk factors for such diseases. METHODS: Plaque occurrence in both carotid arteries, and in the right femoral artery were assessed at baseline by B-mode ultrasound in a population-based sample of 58-year-old men (n=391) with no cardiovascular disease, and varying degrees of obesity and insulin sensitivity at entry. Anthropometry and blood pressure were recorded. Fasting venous blood samples were used for measurement of cardiovascular risk factors. Cardiovascular events occurring during follow-up were obtained by access to register data. RESULTS: Systolic blood pressure, serum triglycerides and waist-hip ratio as well as baseline occurrence of carotid and femoral plaques were associated with events. Logistic multi-variate analyses showed that carotid plaques (OR 2.09, 95% CI 1.05-4.16, p=0.037), femoral plaques (OR 1.99, 95% CI 1.01-3.91, p=0.047) and concomitant presence of carotid, and femoral plaques (OR 2.53, 95% CI 1.23-5.21, p=0.011) were associated with cardiovascular events independently of other risk factors. Plaques occurred in 0-3 arteries and there was a parallel increase in cardiovascular risk (p=0.004). CONCLUSION: Occurrence of carotid or femoral plaques at baseline had similar predictive value for cardiovascular events. Increased plaque burden, with plaques in both carotid and femoral arteries increased the cardiovascular risk further. Hence, the results from this study indicate that ultrasound examination of both the carotid and femoral arteries was the preferred method to predict cardiovascular risk.
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| 44. |
- Davidsson, P., et al.
(författare)
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A proteomic study of the apolipoproteins in LDL subclasses in patients with the metabolic syndrome and type 2 diabetes
- 2005
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Ingår i: J Lipid Res. - 0022-2275. ; 46:9, s. 1999-2006
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Tidskriftsartikel (refereegranskat)abstract
- The exchangeable apolipoproteins present in small, dense LDL (sdLDL) and large, buoyant LDL subclasses were evaluated with a quantitative proteomic approach in patients with the metabolic syndrome and with type 2 diabetes, both with subclinical atherosclerosis and the B LDL phenotype. The analyses included surface-enhanced laser adsorption/ionization, time-of-flight mass spectrometry, and subsequent identification by mass spectrometry or immunoblotting and were carried out in LDL subclasses isolated by ultracentrifugation in deuterium oxide gradients with near physiological salt concentrations. The sdLDLs of both types of patients were enriched in apolipoprotein C-III (apoC-III) and were depleted of apoC-I, apoA-I, and apoE compared with matched healthy controls with the A phenotype. The LDL complexes formed in serum from patients with diabetes with the arterial proteoglycan (PG) versican were also enriched in apoC-III. In addition, there was a significant correlation between the apoC-III content in sdLDL in patients and the apparent affinity of their LDLs for arterial versican. The unique distribution of exchangeable apolipoproteins in the sdLDLs of the patients studied, especially high apoC-III, coupled with the augmented affinity with arterial PGs, may contribute to the strong association of the dyslipidemia of insulin resistance with increased risk for cardiovascular disease.
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| 45. |
- Davidsson, Pia, 1962, et al.
(författare)
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Proteomics of Apolipoproteins and Associated Proteins From Plasma High-Density Lipoproteins.
- 2009
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Ingår i: Arteriosclerosis, thrombosis, and vascular biology. - 1524-4636.
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Tidskriftsartikel (refereegranskat)abstract
- Proteomics studies have extended the list of identified apolipoproteins and associated proteins present in HDL and its subclasses. These proteins appear to cluster around specific functions related to lipid metabolism, inflammation, the immune system, hormone-binding, hemostasis, and antioxidant properties. Small studies suggest that there are substantial differences between the HDL proteome from cardiovascular disease patients and that from controls. Furthermore, dyslipidemia therapy shifts the HDL proteome from patients toward the profile observed in healthy controls. In addition, the proteome of HDL and LDL from patients with insulin resistance and peripheral atherosclerosis show significant differences with that of matched healthy controls. The proteome HDL and LDL density subclasses have apolipoproteins and associated proteins profiles that suggest subclass-specific functions. However, proteomics studies of lipoproteins are few and small and should be interpreted with caution. Nonetheless rapid technical progress in proteomic platforms suggest that soon analysis time will be reduced and precise measurement of identified proteins will be possible. This, combined with controlled purification steps of HDL and its subclasses should provide further information about proteins involved in the particles postulated spectrum of functions, including those believed to be atheroprotective.
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| 46. |
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| 47. |
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| 48. |
- Davidsson, Staffan
(författare)
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Adaptive Driver Information
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New societal requirements and functional growth put new demand on future driver information. Simultaneously, new technology and IT capabilities makes it possible to constantly adapt the information given to the driver for different reasons. Therefore, the aim of this thesis was to obtain an improved understanding, strengthen knowledge of the adaptive control of driver information to understand if, for what reason, when and where to use adaptive driver information (ADI). Also some possible new means to support drivers were suggested.The main purpose of driver information is to support the driver in achieving goals such as a safer, more environmentally friendly, more efficient, legal and enjoyable transportation by providing correct information and feedback.ADI can support the driver throughout development of skill and when performing operational, tactical, and strategic level tasks. Also tasks related to setting goals for the driving task and encouraging good driving behaviour can be supported. ADI can, furthermore help drivers to stay within their comfort zone by visualizing risk or certainty, identify and thereafter adapt how a message is communicated to different personalities, maintain the driver’s mental workload within the safe task load area by reducing demand when it is too high, increase mental workload by extra stimulating task during too low a mental demand, and minimize the risk for mismatches between effort and real demand.ADI changes automatically that may cause new and unpredictable issues reducing the purpose of driver information. These may include: mode confusion, function allocation, over and under trust, locus of control issues, skill degeneration and too low/high mental workload. Research has suggested that the most efficient way to reduce these issues is to make the driver and the automation (the agents) get along together and become team players. The team players should share goals, show intention, show limits of performance, state etcetera. However, for cars, a consumer product, in which visual demand is high, an approach can be where information vanishes when agents have become a “team”. This approach may be called “team building”.Research and industrial contributions has been presented. Several examples of how ADI can be carried out have been suggested and some even illustrated.
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| 49. |
- Davidsson, Simon, 1986-
(författare)
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Global energy transitions : Renewable energy technology and non-renewable resources
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global energy system is dominated by the use of fossil fuels. This system suffers from several problems, such as different environmental issues, while the long-term energy security is sometimes questioned. As an alternative to this situation, a transition to a global energy system based on renewable energy technologies, to a large extent solar and wind energy, is commonly proposed. Constructing the technology needed for such a transition requires resources and how fast this could happen is somewhat disputed. This thesis explores methods to assess the potential constraints for realizing such a transition by looking at potential technology growth rates and outlooks of production of the required natural resources.The thesis is based on three papers presenting case studies that look at growth rates of wind energy as well as future production outlooks of lithium and phosphate rock. Using different types of growth patterns reaching proposed installed capacities of wind power, annual commissioning requirements are investigated, taking account for the limited life expectancy oftechnology. Potential outlooks of mineral production are explored using resource constrained curve-fitting models on global lithium production. A more disaggregated model looking at individual countries are used on phosphate rock production to investigate new perspectives on production outlooks.It is concluded that the growth rates of individual energy technologies affect the resource requirements and prospective constraints on energy transitions. Resource constrained modelling of resource production can provide spans of potential outlooks for future production of resources required for anenergy transition. A higher disaggregation of the modelling can provide new perspectives of potential constraints on future production. These aspects should be further investigated when proposing alternative future energy systems.
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| 50. |
- Davidsson, Åsa, et al.
(författare)
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Property-close Collection of Fat, Oil and Grease (FOG) from Households. – Experiences from a Swedish Case Study.
- 2010
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Ingår i: Proceedings of the IWWG 3rd international symposium on energy from biomass and waste. Venice, Italy 8-11 November 2010. - 9788862650083
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Problems related to content of fat, oil and grease (FOG) in wastewater is an increasing problem in Sweden. FOG can cause clogging in the sewage system and subsequent flooding and disturbance of processes in waste water treatment plants. The problem has previously been mostly been related to release of large quantities of FOG from restaurants and large scale industries which has caused problems in municipal sewage systems. However, similar problems have more recently been detected more frequently in relation to disposal of FOG from households into the sewage. This study evaluated a full-scale experiment with source-separation of FOG from households in a residential area in Malmö, Sweden. Results from the study show that on average 0.35 kg/household and year of FOG was collected during the trial period. Households were positive to the introduction of a source-separation possibility for this waste fraction but only to a smaller extent interested in using designated jars for FOG-collection distributed by landlords. Further investigations are needed to assess the impact from the collection on the sewage net in the multifamily buildings where the system has been introduced.
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